Metric fasteners are fastening and connecting tools that are measured according to the International System of Units (more commonly known as “the metric system” in the United States) instead of the US Customary System (also called the American system).
Metric fasteners are produced for use in applications outside of the sphere of influence of the US and English systems. That difference aside, there are no other meaningful differences between metric and non-metric fasteners. These connective mechanisms are used to join and secure materials together.
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Types of Metric Fasteners
Metric fasteners can be broken down into two types: threaded industrial fasteners and non-threaded industrial fasteners. They are also available in different forms, including metal industrial fasteners, plastic fasteners, or composite industrial fasteners. If needed, conversion charts for the American and metric systems are available from most fastener manufacturers. Threaded metric fasteners, such as nuts, bolts, and screws, contain spiral ridges called threads, which aid in the attachment of the fasteners. Continuous-thread studs, with two nuts applied, are used for flange bolting and are threaded from end to end. Tap-end studs, on the other hand, have a short thread on one end, used for screwing into a tapped hole, and a longer thread on the other. This longer end is called a nut-end and may have either a chamfered or round point. Double-end studs have equal-length threads with chamfered points on both ends and are used for flange bolting or other applications in which torching from both ends is necessary.
Unlike threaded metric fasteners, non-threaded metric fasteners, such as rivet metric fasteners, ring metric fasteners, and pin metric fasteners, do not contain threads. As a result, these metric fasteners can be quickly assembled and removed from components and do not need extra industrial fastening hardware. Bind metric fastener rivets, or pop metric fastener rivets, are inserted into a pre-drilled hole where a rivet gun pulls on a headed-shaft, which passes through the rivet. The shaft breaks or "pops," leaving a bulge on the head of the rivet, which holds the two parts together. Dowel pins can be straight, tapered, rolled, or grooved and provide perfect alignment, holding parts in absolute relation to one another. Most retaining rings need a groove to seal them into position and are stamped both internally and externally. While some of them may be self-locking, both kinds are used to keep parts from slipping or sliding apart. Several other varieties of non-threaded metric fasteners also exist.