Castle Nuts - Metric

Often called an axle nut as this is where they are most commonly found, a castle nut is a slotted hexagon nut with turrets on the top which resemble a castle wall. Castle nuts are used in conjunction with bolts that have holes in the end through which a locking pin can pass to lock the nut into position and prevent any further rotation. The locking pin is usually a split cotter pin, an R clip, a spring pin or a safety wire.

The diameter of the castellated section is slightly smaller than the main wrenching section of the nut (unlike a slotted nut where the diameter of the castellated section is the same as the main wrenching part).

Metric is the most common thread type in production today. Usually specified as M then a number x another number. This signifies the thread diameter and the length of the fastener.

For example, M4 x 30 means that the major thread diameter (the external distance across the outside of the thread) is 4mm and the length is 30mm. Length is usually measured from the underside of the fastener head.

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