Fasteners

Fasteners

US and English fasteners are described by material, head style, and type followed by or preceded by the diameter dash thread count (machine threads only) X length. The diameter and length are in inches except small sizes that usually notated with a # sign, like #12, with a thread count. Nuts used the same diameter and thread count, but obviously drop the length variable. The Society of Automotive Engineers (SAE) maintains a common standard for bolt sizes defined in both English and metric measures. USS is another common standard for non-metric fasteners.

Example: bolt 1/2-13 x 4 has a diameter of 1/2” with a thread count of 13, and a length of 4 inches; this bolt, used in the steering rack assembly, is secured with a 1/2-13 nut (no length designation for nuts)

Metric fasteners

Metric fasteners use thread pitch (the length of each thread in millimeters measured along the shaft of the bolt) rather than threads per inch or per millimeter. The thread pitch is written between the diameter and length (both measured in millimeters) and is separated on each side by an X. Typically the diameter of a metric bolt is preceded by a capital M to designate metric.

* Example: screw M6-1 x 30 is a metric 6 screw with a thread pitch of 1 and a length of 30 mm; this type of screw is used in the steering wheel hardware and is secured with a M6-1 nut (no length designation for nuts)

Socket by bolt/nut size

The following tables show the proper wrench or socket size for various bolt head and nut sizes.

SAE Metric diameter	M6	M8	M10	M12	M14	M16
SAE Wrench or socket size millimeters	10	13	17	19	22	24

SAE English diameter	1/4	5/16	3/8	7/16	1/2	9/16	5/8
SAE Wrench or socket size inches	7/16	1/2	9/16	5/8 bolt 11/16 nut	3/4	13/16 bolt 7/8 nut	15/16

Fastener types

There are many different names for essentially the same type of fastener, depending on the industry, manufacturer, and use. The following terms are most frequently used in FFR instructions and forum discussions.

Allen head bolt