Castle Nuts - BSW

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).

BSW (British Standard Whitworth) is an imperial coarse thread first used in standard production by Joseph Whitworth during the industrial revolution. Whilst it is still used in engineering applications all across the world it is less common in the UK where metric threads have generally taken over.

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