This article is an in depth study of fasteners and their uses.
You will learn more about topics such as:
- What is a fastener?
- What are non-permanent threaded fasteners
- What are permanent fasteners
- How fasteners are made
- And much more …
Chapter One: What is a Fastener?
A fastener is a non-permanent or permanent mechanical tool that rigidly connects or affixes two surfaces or objects together. Non-permanent fasteners can easily be removed without damaging the joined materials. The removal of permanent fasteners might require substantial force and might damage the connected surfaces. Permanent fasteners are designed to be a long lasting form of secure connection.
The wide range of fasteners includes screws, nails, nuts, bolts, and washers that come in different sizes, types, and configurations. Fasteners are one of the most used tools for building, fabricating, and configuring a variety of products and industrial equipment.
Chapter Two: Non-Permanent Threaded Fasteners
There are an endless number of shapes, sizes, lengths, and varieties of fasteners that range from the common nail to huge bolts to hold heavy duty manufacturing equipment in place. They can be generic or specially designed to fit an application. Every industry and manufacturer has a different and unique use for these valuable tools.
The variability between fasteners is due to the extreme forces that are placed on them. The purpose of fasteners is to hold parts, components, and pieces of machinery together in the presence of excessive vibrations and pressure while retaining the ability to disassemble the pieces when necessary.
There are several ways to separate, classify, and categorize fasteners, which include permanent and non-permanent as well as threaded and non-threaded. In the permanent classification are rivets and couplings that cannot be removed. Screws and bolts fall into the threaded classification, while dowel pins and blind fasteners are non-threaded and permanent.
Non-Permanent Threaded Fasteners
Bolts are one of the more common types of fasteners and are used to hold two non-threaded pieces together. The head of a bolt, which comes in several varieties, is attached to the threaded male end. Bolts are classified by their shape and type of head.
Anchor bolts are referred to as “cast in place,” which means they are included in the fabrication of the component or part and are permanently attached to it. Different types of anchor bolts are designed for specific jobs. They are an industrial bolt that has been embedded into concrete for securing columns and supports to foundations.
Arbor bolts have a washer permanently attached to the head and reverse threading. The head of an arbor bolt has a sunken design that creates a ridge on the head. Most arbor bolts have a dark or black finish that distinguishes them from other bolts. They are designed to be used with tools such as a miter saw to keep the blade in place.
Carriage bolts have a smooth head with a square section located underneath that keeps the bolt from turning when secured. The popularity of carriage bolts is due to their ability to be used with any type of material, from stainless steel to wood. They are referred to as plow or coach bolts and get their name from their original use, which was to secure carriages and carriage wheels.
Elevator bolts were invented for use in the construction of elevators and have a large flat head with a square neck underneath to keep the connection secure when vibrations and shock are present. The flat head is designed to fit flat and flush against the surface of the attached material as well as provide load bearing capacity.
Hex Head Bolts
The hex head bolt gets its name from the hexagonal shape of its head that makes it easy to tighten using a box, socket, or crescent wrench. The six sides of the hexagonal shape give the bolt the proper granularity angles for fastening the bolt in difficult locations. The threads on a hex head bolt extend halfway or all the way up to the bolt head with partially threaded bolts having a higher shearing capacity.
Double End Bolts
A double end bolt has threads at both ends without a head. They can have a nut on one end and be inserted into a threaded hole. Double end bolts come with class five threads for the tap end and class 2A threads for the nut end.
Eye bolts have a loop or circular configuration instead of a head. The eye or loop is used for securing electrical lines, holding chains in place, or for guiding ropes. The loop end can be open or closed; the open version does not have a completed loop while the closed version does.
U Shape Bolts
U bolts have two threaded arms connected by a U shape bend without a head. The threaded ends are designed to connect nuts and washers. They are made from carbon, alloy, or stainless steel by cold or hot forging. When the washers and nuts are tightened, they provide clamping force to connect parts or to hold components in place and prevent them from moving.
There are far more bolts than the few listed here. They come in several varieties that include J, flanged, plow, and shoulder to name a few. Bolts are one of the connecting necessities for creating secure and permanent connections.
The construction of screws is similar to that of bolts, with male threads starting from the tip with various types of heads to drive the threads. Unlike bolts, screws do not use nuts to make connections and require some form of internal threads to sustain a grip. In most cases, screws are self threading or self tapping, meaning they create the threads into the material where they are being placed.
Much like bolts, there are an endless number of screws designed to fit specific jobs. Regardless of the different types, screws have a pointed or flat tip with tips that can be threaded or drill bit.
Self Drilling Screw
Self drilling screws create internal threading when they are installed. They are fully threaded from the tip to the head, with threads that are harder and more rigid than the materials they are joining. Self drilling screws have a variety of tips in unique shapes. Notched tips or drill bit tips can easily be installed and create their own space in the substrate.
Sheet Metal Screw
Sheet metal screws are designed to join metal pieces and have a threaded shank that covers its entire length with a rounded or flat head. The tip of a sheet metal screw is sharp so that it can pierce the substrate of a piece of metal. Sheet metal screws can be self drilling and self tapping. They are made from hardened metals that are capable of drilling into a metal surface.
A machine screw is similar to a bolt and has a diameter of 0.75 inches or less. Due to their size restriction, established by the American Society of Mechanical Engineers (ASME), machine screws are smaller than other types of screws. When joining or connecting two pieces of metal, machine screws are inserted into threaded holes. The size of the threads, helical ridges, remain the same from the top of the screw to the tip.
A dowel screw is like a double end bolt with both ends being threaded with a wood screw tip. They do not have a head and can be inserted into pre-drilled holes or create their own threading. A dowel screw functions like a dowel with threads but forms a more permanent bond between the pieces being joined. They are normally used for woodworking projects and can be threaded from end to end without a gap.=
A nut is a fastener with an external thread that is used with a mating bolt that is of the same size. There are several varieties of nuts that include box and hex types as well as several other specialty kinds, configurations, and designs.
Cap nuts are known as dome or acorn nuts and have the shape of a dome on the closed end to protect the bolt-nut assembly.
Castle nuts have notches on one end that allow for the insertion of a pin.
Welded nuts are welded onto the surface and are used to fasten hard to reach places.
The hex nut is one of the most common types of nuts and is easy to install.
Nylon Lock Nuts
Nylon lock nuts have the same shape as a hex nut but have a nylon collar that locks into the bolt to prevent loosening.Flange Nuts
A flange nut is like a flange bolt and flange screw with a wide flange at one side of the nut to distribute pressure to the piece being secured.
The image below contains a few of the various types of nuts. As with every type of connector, there are numerous nuts designed to match the many types of bolts.
A distinguishing feature between the various types of screws and bolts are their heads, which are designed to fulfill a particular function. The variety of heads is as expansive as the different types of screws. A few are listed below.
Flat screw heads
Flat screw heads are countersunk and fit flush with the secured surface. They have varying angles from the top of the head to the threads.
Raised screw heads
Raised head or oval head are similar to flat head screws but have a domed shaped head.
Bugle screw heads
Bugle screw heads have a curved shape below the head instead of an angle to prevent damage to the surface they are connecting.
Domed screw heads
Domed screw heads provided a larger surface for the screw to stop turning.
Truss screw heads
A truss screw head is wide but low profile with a large surface area. The head is slightly rounded but wider.
Binding screw heads
Binding screw heads are similar to a pan head but thicker with a deeper slot, and they have a 10% larger bearing surface.
Flange screw heads
Flange screw heads provide a wide surface area and have an attached washer built into the screw head.
Pan screw heads
A pan head is slightly rounded with short vertical sides. The head is similar to the head on a carriage bolt without the square shape underneath the head.
The drive part of a bolt or screw transfers torque or force from the driver to the bolt or screw and forces it into the material. There are several types of drivers as well as specialty drivers designed to fit unusual or unique applications. Listed below are a few common drivers.
The slotted driver is the traditional type that is designed for flat head screw drivers. With a lack of centering, the bit can slip out of a slot head.
A Phillips head has a simple cross shape that offers more surface area for turning the bolt or screw, which reduces the necessary force to insert the bolt or screw.
A pozi drive is like a Phillips drive but has extra grooves to form a star shape look.
A torque drive has a greater surface area, which makes it easier to turn and reduces the amount of slippage. A higher amount of force can be applied with a torque drive, making the connection more secure.
Hexagonal Interior Driver
The hexagonal interior head can have an Allen or hex screwdriver inserted to attach it. This head shape allows for greater surface area for the transferring of force.
Hexagonal Exterior Driver
This form of hex drive allows for the use of sockets and spanners and has a large contact surface for applying increased force.
Some screw heads combine two different types of drivers to make them compatible with two types of drivers. A common combination is flat and Phillips.
Square Recessed Driver
Square recessed drivers have a square centered head that works to prevent cam outs and slippage. They are driven by a square tapered driver.
One Way Driver
The one way driver head is a variation of the slotted or Phillips driver and can be tightened with a standard screwdriver. Since they are one way, they require a special tool to remove them.
Chapter Three: Permanent Fasteners
Permanent fasteners come in several forms and are designed to connect surfaces and not be removed. Permanent fasteners do not have threads and can be quickly installed without the need for extra fastening components. Wooden dowels, nails, various types of rivets, and varieties of pins are classified as permanent fasteners.
The removal of a permanent fastener requires force, which may damage the surface of the connected pieces. The disassembly of permanently connected materials is time consuming and requires a great deal of effort.
The unique quality of nails is their smooth shaft that is designed to connect surfaces by being driven in by the force of a hammer or nail gun. The common nail is divided into the head, shank or shaft, point, and gripper marks, which are marks incised into the shank near the head for extra gripping.
Common nails are used for carpentry and construction. They have a heavy shank for sturdy support for any type of building or structural project. Common nails are functional and not used for their appearance. They are noted for their strength, endurance, and reliability.
Box nails are similar to common nails but have a thinner shaft for use with thin wood and plastics. Unlike common nails, box nails are not sturdy or strong due to the structure of their shaft but are ideal for use in finishing projects such as cabinets and paneling.
Brad nails are small with a thin head that is almost invisible when driven into wood. The majority of brads have an 18 gauge diameter, which makes them easy to mask on trim and molding. Their thin design makes them ideal for use with materials that would be split by larger diameter nails.
Though brad nails and finishing nails are similar, finishing nails are large with gauges ranging between 15 and 16. They are used in projects where strong holding is necessary, such as for items that may hang from the walls or ceiling. Regardless of the difference in size between brads and finishing nails, finishing nails have the same small head as brads but with greater holding power.
Cut nails have a blunt point and tapered shank to help reduce splitting. They have a four sided design that is similar to a square that is resistant to bending when being installed. When cut nails are placed and connected, they are extremely difficult to remove.
Drywall nails have to be specially designed due to the types of materials with which they are used. They have rings along the shaft that may look like the threads of a screw, which increases their gripping power and keeps them from slipping out. Since drywall nails are designed to secure walls, they are driven into drywall such that they are flat with the surface and can easily be covered with drywall tape.
There are several varieties of flooring nails with designs that enhance their gripping power and strength. Some flooring nails are like drywall nails with rings on the shank that help them fit more securely. The types of flooring nails include ones with spiral shanks to increase the tightness of their fit.
Concrete nails are some of the sturdiest and most durable types of nails. They have a thick shank that is made from hardened steel that is capable of punching a hole in a cinder block. They have fluted shafts to make them cling snuggly to brick, concrete, and masonry.
The special feature of roofing nails is their wide head that is designed to seal their hole and prevent leaks. They have a ringed or twisted shank to increase their holding power as well as prevent them from loosening. Roofing nails are galvanized to resist corrosion and rusting.
Nail Design Features
The sizes of nails vary from one inch to over five inches. Nails that are six inches or longer are classified as spikes. The gauge of a nail is the descriptor of its diameter with higher gauges being smaller diameters. Nail heads can be flat, checkered, or countersink, which is a conical shape to be pushed out of sight.
Nail points are dull, diamond, or blunt. Dull points prevent wood from splitting, and diamond points are partially blunt. The best type of point is blunt, and it is the most commonly used.
The shanks of nails are normally smooth but may have adjustments to increase their holding strength. Ringed shanks have a series of raised rings for a more secure and tighter fit. Barbed shanks are the most secure and are ideal for rough carpentry on harder and more dense wood materials. Spiral shanks are somewhat like a screw and twist as they are driven in.
For ease of installation, modern nails are covered with some form of coating that lubricates the shank. Galvanization with zinc and vinyl are forms of coatings that make driving nails easier. Though coatings make it easier to insert nails, it does not detract from the nails holding power.
The original classification for the length of nails was established in England and determined by the price of 100 nails where the “d” stood for the English pence or penny, a measuring system referred to as penny size. This age-old method for classifying nails has continued down the centuries and is still used in England and the United States with a number and the letter “d” to determine the length of a nail.
Rivets are light weight and have excellent support against shearing forces. With a head at each end, rivets can support a certain amount of axial loads and are installed using a rivet gun without the need for holes being drilled or threads being created. Of the forms of permanent fasteners, rivets are the most permanent, and they have a wide range of strength to weight ratio types.
The solid rivet is one of the oldest forms of fasteners, and it has a very basic design and construction that consists of a shaft and head. They are installed using an impact hammer, riveter gun, or compression tool. Solid rivet drivers use hydraulic, pneumatic, or electromagnetic force to drive, deform, and place a rivet. They are used where reliability and safety are required.
The structure of a tubular rivet is very similar to that of a solid rivet but with a partial tube at the tip. The tube at the end reduces the amount of force required to install the rivet. When the rivet is driven in, the tubular portion rolls outward to seal the rivet in place. A wide range of materials are used to make tubular rivets, this includes steel, stainless steel, aluminum, brass, and copper. The material a rivet is made of determines its use.
Blind rivets, or pop rivets, are a tubular rivet with a mandrel down the center. They are installed where there isn’t access to the back side of the materials being joined. The rivet is inserted into a hole and the mandrel is pulled out using a special tool. As the mandrel leaves, it folds the tube against the side of the inner surface. Blind rivets can be self drilling, self tapping, or speed fastening.
A drive rivet is a form of blind rivet with a shorter mandrel, and it is hammered in to make the connection. As the rivet is hammered, the shank expands to seal the connection on the inner surface of the material.
A split rivet, or bifurcated rivet, is a self-piercing rivet that has split legs attached to the head of the rivet. The pre-split shaft is placed into a hole and pounded. The force of the pounding causes the legs to spread and secure the connection.
Anchors are a special form of fastener designed to secure metal components to concrete, epoxy, vinylester, and polyester resin. They are installed when the concrete is drying, or they are inserted into it after it has hardened. Anchors come in designs to fit the item to be secured and the application. The benefit of anchors is their ability to transfer tensile strength and shear force to the substrate.
There are two types of anchors: mechanical and chemical (bonded). Anchors are required to resist pullout and shear forces with pullout forces acting against the axis of the fastener and shear forces acting at right angles to the fastener.
Mechanical anchors are inserted into a hole while chemical anchors are secured with a form of adhesive.
Types of anchors include but are not limited to:
Acoustical anchors are designed to hold wiring in place on concrete or masonry.
Double expansion shield
Double expansion anchors expand as they are screwed in and are a form of mechanical anchor.
Hammer drive pin
Hammer drive pin anchors are light duty anchors and are pounded into the surface until the nail of the anchor is flush with the surface.
Screw in anchors are made of a variety of materials that include plastic, metal, or fibers. They have a Phillips style head that screws into a pre-drilled hole.
The main use of inserts is as reinforcement for fasteners. They are placed into a hole for a small stud or bolt to be screwed in to restore strength and stability to a joint or connection. Inserts, also known as threaded bushings, are used to repair stripped threads, provide threads for soft materials, or simply to add threads.
Externally Threaded Inserts
Externally threaded inserts or self tapping inserts are cylindrical metal bushings with external and internal threads that are designed to cut through as they are screwed into a hole.
Internally Threaded Inserts
Internally threaded inserts have internal threads that expand against the sides of a pre-drilled hole as they are screwed in. The body of the insert expands against the surface of the hole to form a firm secure grip.
Key Locking Inserts
Key locking inserts are internally and externally threaded with a vertical key attached to the top of the insert. They are installed into a pre-drilled hole with a key driven into the tapped threads of the parent to provide a mechanical lock. Key locking inserts reinforce weak parent materials.
Press In Inserts
Press in inserts are designed to be used in hard plastics and require a special insertion tool, which applies a high frequency ultrasonic sound wave to the insert as it is pressed into a hole in the plastic material. The heat from the ultrasonic waves melts the plastic and locks the insert in place.
Helical Screw Inserts
Helical screw thread inserts are made from diamond shaped coiled wire. The insert is screwed into a threaded hole that is stronger than the parent material to repair a damaged threaded hole.
Blind Threaded Stud Inserts
Blind threaded stud inserts have a round knurled body with a projecting machine screw threaded stud. The stud is inserted into a pre-drilled hole using a special insertion tool. As the threaded portion pulls up, the back of the body of the insert bulbs out to form a lock around the hole.
Retaining rings are metal fasteners that are used to hold a shaft or assembly in place, and they come in a wide variety of styles, configurations, designs, and sizes to fit the needs of an application. They are a permanent type of fastener that is discarded when they are no longer required.
The typical retaining ring is a circular piece of metal that sits in a groove on a housing or shaft. They can be internally or externally installed as can be seen in the diagram below.
The convenience of retaining rings removes the need for complex machining processes that are costly and time consuming. They streamline assembly operations and can replace bolts on gear assemblies, eliminating the need to drill tapping holes and helping to simplify installation processes.
Chapter Four: Types of Washers
Washers are a small, circular, metal disc in the shape of an annulus, halo, donut, or ring that is used to distribute the force of a screw, bolt, or nut. They can relieve friction, stop leakages, maintain tension, prevent corrosion, and serve as a spacer or separator. The wide and varied uses of washers has made them a necessity in a number of applications.
The many varieties of washers are further enhanced by the many types of materials used to produce them, which include zinc, copper, brass, iron, carbon steel, and stainless steel. Certain applications require specialty washers that are made from non-metallic materials such as plastic, rubber, ceramics, and phenolic.
The types of washers can be divided into three categories, which are plain, spring, and lock. In each of the categories are specialized forms that are designed to serve a specific or unusual function.
The many functions of washers include:
- Reduction of friction
- Distribution of pressure
- Blockage, cessation, or elimination of leakage
- Separation of components
- Enhancement and securing of connections from vibrations and shock
Types of Washers
The purpose of plain washers is to isolate the material being secured from a bolt, screw, or nut. They may serve the purpose of insulation or be a means of protecting the substrate. Another function of plain washers is to distribute the load by increasing the surface area that contacts the substrate. If a hole is too large, a washer can make up for the size difference.
A flat washer is referred to as type A and is for general use in correcting hole size and distributing the load.
Torque washers are used for woodworking projects with bolts to prevent them from spinning when the nut is being connected.
Fender washers have a small inner diameter with a much larger outer diameter as a way to distribute force over a large area, especially with thin metals.
C Type Washer
A C washer has a section cut out of a flat washer that allows it to be inserted when a fastener is not completely disconnected. The space allows a C washer to be slipped in place.
Finishing washers are used with countersunk screws as a means of holding them in place.
Square washers, known as blind rivet washers, fit into slots and channels and have flat sides that keep them from rotating. They are wider and thicker than round washers, which makes them an excellent method for distributing a load. They come in several sizes and dimensions to perfectly fit any bolt or screw.
A spring washer is capable of acting like a spring due to a slight change in their circular structure that gives them axial flexibility and elasticity. Spring washers are designed to stop possible loosening or release of tension in the fastener due to shock, vibration, or shaking of the joined pieces.
Belleville Spring Washer
Belleville spring washers look like a hollow cone with the top of the cone removed. They have great flexibility in the axial direction and support axial forces with little deflection. Belleville spring washers can be found in applications that are subject to thermal expansion.
Crescent Spring Washer
A crescent washer is a plain flat washer that has been moderately bent or curved to give it the appearance of a crescent. This type of washer is slightly capable of absorbing axial forces and is only used in small movement applications.
Dome Spring Washer
Dome spring washers have the shape of a dome with a hole in the top. They have a very high load capacity with a small deflection range and have ground curves to form a flatter load bearing surface. Dome spring washers are used for their ability to form a flatter surface.
Wave Spring Washer
Wave spring washers are used in applications where there is thermal expansion and contraction. They are designed for minimal axial space and for a modest working range. Their uniform waves ensure an optimal load rate and loaded waves.
Locking washers are an excellent tool for locking bolts, nuts, and screws in place where there is a chance of a connection becoming loose due to friction, shock, rotation, or vibrations. They exert a spring tension on a fastener that keeps it from loosening. Locking washers are placed beneath the fastener as an extra measure of security.
External Teeth Washers
The teeth for an external locking washer are around the circumference of the washer and extend radially outward. When the nut, bolt, or screw is tightened, the external teeth bite into the surface of the substrate to hold the fastener tightly in place.
Internal Teeth Washers
For an internal tooth locking washer, the teeth are on the inner diameter of the washer and extend toward the center of the washer. Just like in the external tooth locking washer, as the fastener is tightened, internal teeth dig into the substrate to lock the fastener in place.
Split Lock Washers
Split lock washers have helical shaped split rings that exert spring force on the fastener that creates increased friction and motion resistance. A split lock washer looks like a flat washer that has been cut and the two ends bent in opposing directions. When the fastener is tightened in place, the two split ends lodge snuggling in a firm, secure mating position.
Tab Locking Washers
A tab locking washer looks like a flat washer with a single tab extended on the inner side of the hole in the washer. They can be manufactured with a single tab or multiple tabs depending on the application. Tab lock washers are designed to fit around bolts or nuts and are made to lay flat. They lock the fastener in place and are ideal for drastically hot conditions or heavy vibrations.
Chapter Five: How Fasteners are Made
There is more than one process used to produce nuts, bolts, clips, screws, and all other fastener types. The three methods that are used the most are machining, cold forging, and hot forging. (These are commonly used methods for forming and producing metal parts.)
The choice of which method to use to produce a fastener depends on the type, metal, and quantity with some methods producing greater quantities than others. Metal type plays a major role in the forming method since some metals are more pliable and have greater elasticity.
How Fasteners are Made
The machining process is a method for deforming metals to create parts and components. By cutting, drilling, turning, milling, and grinding a piece of metal, it can be deformed and shaped to fit a desired pattern or form. Unlike molding and casting, machining is a process that works the metal at room temperature or slightly above. Though the metal may heat up due to friction, heat is not a part of the process.
Machining begins with a round or hexagonal piece of metal. During the machining process, the metal piece, the workpiece, is threaded and shanked to meet the required geometry of the final part. Machining can involve several processes at once, which are performed on a computer numerical control (CNC) machine; this helps in speeding up the process.
The benefits of machining include precision, exceptional tolerances, and the ability to produce complex geometries. It is a time consuming process that is ideal for short runs of minimal quantities.
Of the various methods for creating fasteners, cold forming, or cold roll forming, is the most common due to its speed and reduction of waste. Like machining, it is performed at or near room temperature to produce large quantities of fasteners in a fast, efficient, consistent, and cost effective way.
Cold forming begins with a coil of wire that is processed, straightened, and sheared to the length required by the final part. The prepared pieces are fed into a rolling machine to complete the forming process and add intricate and precise details. The pressure applied to the workpiece maintains the original grain structure of the metal, which improves the tensile strength of the fastener.
The types of cold forming are upsetting or heading, extrusion, and rolling. In the upsetting process, the workpiece is upset at one end to increase the area's cross section. With cold forming extrusion, compressive force is applied that causes the metal to produce deformation heat; this force can be applied at various angles to the workpiece. Cold roll forming also applies pressure to the workpiece to achieve the desired shape.
Hot forging is used when fasteners cannot be produced using machining or cold forming. A key part of hot forging is the heating of the workpiece. In the heating process, the workpiece is heated to its recrystallization temperature, which can be as high as 1200o C or 2192o F. The temperature at which the metal is heated allows it to maintain its deformed shape as it cools.
During the forming and shaping process, the grain structure of the metal is broken down and homogenized into a finer grain, a process that enhances its strength, ductility, and toughness. Since hot forging produces very little scrap and waste, it is one of the most efficient metal forming methods.
Metals Used to Make Fasteners
When choosing the type of metal or fastener for an application, there are certain factors that have to be considered; these include the location in which it will be used, the environmental conditions, and the amount of moisture and heat. Though heavier metals may seem appropriate, they can fail if placed in the wrong conditions.
Of the various metals used to produce fasteners, steel is the most common. It can be plain or have surface treatments such as galvanization.
Steel fasteners are made of steel grades 2, 5, 8, and alloyed steel.
- Grade 2: Most common and least expensive
- Grade 5: Hardened to increase strength and used in automotive applications
- Grade 8: Hardest of the three and used in demanding and stressful applications
Alloyed steel fasteners are exceptionally strong and have been heat treated. They are normally coated with a dull black finish.
Stainless steel is ideal for fasteners because of its corrosion and rust resistance, and it maintains these characteristics if scratched during installation. There are several grades of stainless steel with each grade having different properties.
- 18-8 Stainless Steel: The most common stainless steel.
- 316 Stainless Steel: Exceptionally resistant to corrosion and ideal for salt water and chlorine environments.
- 410 Stainless Steel: Harder than 18-8 but less resistant to corrosion.
Aluminum is normally alloyed with another metal when used for producing fasteners. Rivets are commonly made from 5000 series aluminum. The added alloys increase aluminum’s strength and raise its melting point.
Brass is an alloy of zinc and copper. It is a soft metal with corrosion resistance and electrical conductivity. Brass is mainly used for its appearance.
Bronze is an alloy of copper, tin, and a small amount of silicon. It has superior corrosion resistance and strength. Bronze can be used as a non-permanent fastener because of its re-fastening capabilities.
- A fastener is a non-permanent or permanent mechanical tool that rigidly joins, or affixes two surfaces or objects together.
- There are an endless number of shapes, sizes, lengths, and varieties of fasteners that range from the common nail to huge bolts to hold heavy duty manufacturing equipment in place.
- The group of permanent fasteners do not have threads and can be quickly installed without the need of extra fastening components.
- Washers relieve friction, stop leakages, maintain tension, prevent corrosion, and serve as a spacer or separator.
- The three methods used to produce fasteners are machining, cold forging, and hot forging; these are commonly used methods for forming and producing metal parts.