Castle Nut

A castle nut is a hex nut with slots cut into the top. A split pin or cotter pin passes through the slots and a hole in the bolt to lock the nut in place.

A castle nut takes a cotter pin through the slots in its crown to stop it turning on a drilled shank. It matches a bolt or stud of the same thread that has a cross hole for the pin. The pin is bent over after fitting to hold the nut in place.

Hot-dipped galvanising gives a thick zinc coating for outdoor and corrosive conditions. Plain finish is bare metal with no added coating. PTFE coating provides low friction and some chemical resistance.

This kind of part is often made in steel, stainless steel 304, stainless steel 316 or brass. Stainless steel 316 offers better corrosion resistance than 304 for marine or chemical use. Brass is chosen where a non-sparking or decorative finish is wanted.

This is a general guide to checking this kind of part. It says nothing about any supplier's parts.

Ask for a certificate of conformance for the material and finish. On receipt, check the slot width and depth for a correct fit with the split pin. Confirm the thread form and the finish for damage or bare patches.