Bolts

Bolts

Bolts are inserted into industrial material in multiple ways. Bolts can be engaged with the use of handheld screwdrivers, high pressure drills and allen wrenches. The nut, which attaches to the end of the shank, is almost always hexagonal in shape. The military and aircraft industries have specific bolt standards that require special anti-corrosive coatings and materials. These bolts are tested under more rigorous conditions, and therefore, are the preferred standard of the respective industries. Bolts are used in nearly every industry, specifically in building construction and automotive manufacturing. In the United States, most bolts are measured by the American Measuring System. However, Europe and Asia use the Metric System. Recently, metric bolts have become more popular in the United States because of international businesses that need parts that are compatible with products from other countries. Bolts come in many different sizes, shapes and materials. Anchor bolts, J bolts, stud bolts, expansion bolts, lag bolts, U bolts, eye bolts, hex bolts and shoulder bolts all have different specific uses and defining shapes and are commonly found in warehouse stock inventory.

The manufacturing process to create standard metal bolts out of stainless steel, titanium or aluminum takes many steps. Stainless steel is often chosen for the manufacturing of bolts because of its strength. First, a steel wire rod is heated in a furnace for 30 hours and bathed in sulfuric acid to remove any rust particles. It is also coated with phosphate that prevents rusting and acts as a lubricant. The rods are then formed by cold forging, where the rod is shaped at room temperature using high pressure. It is forced through dyes and shaped into long, perfectly round rods. After they are cut into shorter pieces, the rods go through a dye that shapes a head on one end. The threading on the other end is done by another cold forging method using high pressure rollers that press in the thread pattern.

Bolt manufacturers designate bolts by the major diameter of the external thread and the pitch measurement. A thread is a ridge that wraps around the outside of a cylinder in a helical pattern. The ridge itself is called the crest, while the space between the ridges is called the root. Threads are set at an angle to the axis of the bolt and slope either upward to the right (for right-hand threaded screws) or upward to the left (for left-handed threaded screws). The slope of the thread is known as the helix angle. The thread forms a V-shaped angle between the crest, called the thread angle, which is determined by fastener engineers. The distance from one crest of one thread to another crest is called the pitch and is measured along the axis of the thread with a thread pitch gauge. Bolts are further classified by bolt manufacturers according to the type of the top portion, called the head. The head comes in a variety of shapes and styles. Flat heads are used where finished surfaces require a flush face. Round heads were commonly used in the past, but are now being replaced by newer designs, such as pan heads. Oval heads require the hole to be countersunk. Binding heads are undercut, bound and eliminate the fraying of stranded wire in electrical and radio work. Truss heads, also known as oven, stove or oval binding heads, are used to cover large diameter clearance holes in sheet metal.

Anchor bolts are generally embedded in concrete and used to anchor columns or other supports to a foundation or for construction and in securing traffic signal poles. U bolts are named for their shape-they are bent bolts with threads at both ends. They may be round, square or semi-round and used when suspended items need to be attached to the surface of something. U bolts are common in the construction and automotive industries. Eye bolts are threaded at one end and have a circular eye at the other, instead of a head. The eye is used to guide a cable, rope or chain for lifting purposes. Eye bolts are common in aircraft construction. J bolts are also named for their shape, a letter J, or half of a U bolt. They are used as cast-in-place anchor bolts and often made of steel or titanium. Stud bolts are round metal bars with screw threads at both ends or on the whole thing. Expansion bolts consist of a taper-headed bolt, lead sleeve, metal cone and a nut. They are used to secure theatre, auditorium, stadium and classroom seating to the floor. They have attachments that expand as the bolt is driven into a surface. Lag bolts are heavy woodscrews that have a hexagonal or square head and are usually driven into wooden beams or posts by a wrench. Hex bolts are very common and usually made of metal and used with a washer. They are named for the six sides on the bolt head. Finally, shoulder bolts pivot mounting shafts that are not threaded all the way up-it stops before the head, leaving a smooth-sided shaft that is usually a little wider than the threaded part. They can be square or round and are generally made out of stainless steel.

Image Provided by Superbolt, Inc.

Images Provided by Elgin Fastener Group

Bolt Types

• Aircraft bolts are made from cadmium to prevent corrosion and have threads rolled or pressed into the bolt, which make the bolt much stronger than the cut threads in a hardware bolt. Aircraft bolts are also tested in smaller batches for quality and are used primarily by the military and aircraft industries.
• Anchor bolts are long "L" shaped-style bolts that are set in concrete to anchor columns or other supports to a foundation.
• Bolt manufacturers produce bolts for various uses.
• Carriage bolts are bolts with a round head and are used for timber. Carriage bolts are threaded on only part of the shank and are inserted into pre-drilled holes.
  
• Expansion bolts are multi-component fasteners that expand upon installation to provide secure fastening in materials that do not permit reliable thread formation as is needed for other types of bolts. 
• Eye bolts are bolts with an eye at one end in place of a standard head.
• Hex bolts are threaded mechanical fasteners that have six sided heads and are often used in conjunction with a hex nut to adjoin two surfaces or objects securely.
• Industrial bolts are mechanical fasteners with  threaded bodies which are driven through two adjacent surfaces for the purpose of adjoining them securely in high stress situations.
• J bolts are fasteners shaped like the English letter from which its name is derived and used in a variety of applications to anchor an object or surface to another surface.
• Lag bolts are heavy woodscrews that have a square or hexagonal head, which is driven in by a wrench.
• Metric bolts are used by the international community and are measured using the metric system as their defining classification.
• Reduced shank bolts are bolts whose shank diameter is smaller than the normal dimensions for the bolt.
• Shoulder bolts are straight mechanical fasteners with partially threaded shanks that allow their use in situations where pivoting or movement is necessary, though they may also be used to prevent motion where fully threaded bolts may loosen.
  
• Stainless steel bolts are used for applications where strength and resistance to corrosion is desired.
• Step lock bolts are made to resist vibration loosening. Step lock bolts have several portions of horizontal threads called steps.
  
• Stove bolts are small-sized machine bolts.
• Stud bolts are un-headed fasteners with a fully or partially threaded body which, with additional hardware, can secure two adjacent objects or surfaces. Unlike many types of bolts, this particular style is not driven into an object or surface, but passed completely through. Nuts or flanges on either end of the bolt then hold the two objects together.
• U-bolts are U-shaped bars that have bolts and threads at both ends but not in the middle. U-bolts are primarily used in suspension areas of vehicles.  

Bolt Terms

Angle Controlled Tightening - A tightening method in which the surfaces are pulled together by tightening the fastener with a pre-selected (snug) torque. The nut is given an extra measured rotation, further tightening the fastener, often beyond its yield point to ensure the achievement of a precise preload.
 
Anti-Friction (AF) Coating - Dry lubricants that are comprised of suspensions of solid lubricants of small particle size, such as graphite or PTFE.
 
Anti-Seize Compound - A compound that is applied to the threads of fasteners and whose purpose depends on the application. Anti-seize compounds can prevent galling or mating surfaces, improve corrosion resistance or provide a barrier to water penetration by sealing the threads.
 
Bearing Stress - The surface pressure acting on a joint face, resulting from the clamping force applied by a fastener.
 
Black - A term that refers to the comparatively wider tolerances employed in the manufacturing of nuts and bolts, not necessarily the color of the surface finish.
 
Clamping Force - The compressive force exerted on a joint by a fastener.
 
Class of Fit - The measure of the degree of fit between mating external and internal threads. There are three main Classes of Fit for metric screw threads: fine, medium and coarse.
 
Creep - The permanent deformation of a bolt or other fastener resulting from the application of stress and heat.

Cut Threading - Forming threads on a fastener by cutting away and actually removing the unneeded metal.

Eccentricity - The degree of difference between the centers of the surface of a bolt at different points.

Fatigue Strength - The fracture resistance of bolts during subjection to stress variations.

Grip - The thickness of all materials that a bolt is designed to secure.
 
Head - The top portion of a bolt. A head also refers to the portion of a fastener that forms its largest diameter.

Joint - The material(s) that the fastener (bolt) connects together.
 
Nut - A small metal piece with a hole in the center that fits over a bolt or over the end of a bolt. Nuts are often hexagonal (6-sided) in shape.
 
Pull-Out - The amount of force required to pull the fastener out of the base material.
 
Shank - The portion of a headed fastener that lies between the head and the point.
 
Tensile Strength - The amount of longitudinal load/elongation a fastener can withstand without failure of the fastener or joint.
 
Thread - A raised helical pattern going around the shank of a bolt. The thread is measured by pitch, which is the distance from one peak of the thread to the next, expressed in mm or threads per inch.
 
Ultimate Torque - The amount of force at which a threaded fastener, an insert or nut begins to strip or otherwise fail in a joint.