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Dimensions of fasteners

For many reasons manufacturers of cars more and more widely used metric fasteners. However, it is important to know the difference between used sometimes standard (also called American or standard SAE) and more universal system of measures metric fixture as, despite the external similarity, they are not interchangeable.

All bolts, both standard and metric classified according to diameter, length and thread pitch. For example, the standard bolt 1/2 - 13 x 1 has a half-inch in diameter, 13 threads per inch and a length of 1 inch. Metric M12 - 1.75 x 25 has a diameter of 12 mm, the thread pitch of 1.75 mm (the distance between adjacent coils) and a length of 25 mm. Both bolts are almost identical in appearance but are not interchangeable.

In addition to these features both metric and standard bolts can be identified by visual inspection of the head. To begin, the distance between the flats of the bolt head metric measured in mm, while the standard - in inches (the same is true for nuts). As a result, the standard wrench is not suitable for use with metric fasteners, and vice versa. In addition, the heads of most of the standard bolts usually are available the radial notches defining the maximum admissible effort of a tightening bolt (degree of strength). The greater the number of notches, the higher the permissible force (typically used on vehicles with bolts degree of strength from 0 to 5). Strength class of metric bolts is defined by a numeric code. Code numbers are usually cast as standard on the bolt head (on cars bolts commonly used classes 8.8, 9.8 and 10.9).

Marking a class of durability of bolts (top - standard / SAE / SS, at the bottom - metric).

Also on the labels of strength class standard nuts can be distinguished from the metric. For identification standard nuts strength applied dot marks stamped on one of the end surfaces of the nut, while marking metric nuts made using again figures. The greater the number of points, or the higher the value of the digital code, the higher the permissible force tightening the nut.

End faces of metric hairpins also are marked in accordance with the class of their strength. Large labeled hairpin digital code, whereas the smaller marking is in the form of a geometric figure.

It should be noted that a significant portion of the holder, in particular the class of strength from 0 to 2, generally not labeled. In this case, the only way to distinguish a standard fixture of the metric is to measure the thread pitch or threads with comparing uniquely identified.

Standard hardware is often called, as opposed to metric, SAE standard fasteners, however, it should be remembered that under the SAE only small fixture gets. Close to the non-metric threaded fasteners is a fixture of the American standard (USS).

Since the hardware of the same geometrical size (both standard and metric) can be different strength classes, the replacement car bolts, nuts and studs should be given to matching the strength class of the newly established fixture strength class old.

Marking a class of durability standard hex nuts

Strength class	Identification of the class
Hex Nut - strength class 5
Hex Nut - strength class 8

Marking a class of durability of metric hex nuts

Strength class	Identification of the class
Hex Nut - strength class 9
Hex Nut - Strength class 10

Marking a class of durability of metric studs

Dimensions / marking strength class standard (SAE and USS) bolts

G - Marking strength class L - length (in inches) T - Pitch (number of threads per inch) D - The nominal diameter (in inches)

Dimensions / marking strength class of metric bolts

P - Strength class L - Length (mm) T - Thread pitch (the distance between adjacent coils in mm) D - The nominal diameter (in mm)

Dimensions of metric threads

Dimensions pipe threads

Thread size American standard