FMW Fasteners

Inch Fasteners

A common nomenclature format for Inch or US Fastener products to follow is a “size description” then followed by a “part description.”  You will see many variations that will sometimes invert one before the other, but as long as you understand the components of both, you can accurately describe the item.

The size description is made up of the diameter, in some cases followed by threads per inch and then the length.

Example:  5/16-18 x 2 ½ (5/16 = diameter 18=threads per inch 2 ½=length)

The part description will usually contain the head type and drive type followed by the type of product and ending with any type of plating the part may have.

Example:  Slotted Hex Machine Screw Zinc (Slotted Hex = head type/drive type Machine Screw= type of product Zinc=plating)

There are many variations and abbreviations used by different manufacturers but if you keep in mind the two distinct areas of information (size information + part information) required to accurately describe the fastener, you can usually decipher even the most unique descriptions.

Note:  Sometimes, threads per inch are specified as course thread or fine thread, rather than giving the actual thread count. This is usually done with an abbreviation at the end or occasionally in front of the diameter and length.

Example:  5/16 x 2 ½ CT or 5/16 x 2 ½ UNC

Metric Fasteners

Metric fastener products follow a similar format as described above with both a size description and a part description required to accurately describe the item.  One major difference is that metric products do not have a value for “threads per inch.”  Instead, they use “thread pitch,” which technically is the length of each thread in millimeters measured along the bolt shank.  Thread pitch follows the bolt diameter, separated by a dash or an x.

Example:  M12-1.75 x 60 or M12 x 1.75 x 60 (M12=diameter 1.75=Thread Pitch 60=Length)