castellated nut

A common application of this is when used to secure a castellated nut.

From old leather horse harness to pins to keep castellated nuts in place on the tractor.

Castellated nuts are used in low-torque applications, such as holding a wheel bearing in place.

A castellated nut, also called a castle nut or slotted nut, is a nut with slots (notches) cut into one end.

The stainless steel split pins were then removed from the 14 castellated nuts and the main caps drawn off with a length of 1/2" BSF threaded rod and a large section of channel.

The rear wheel carried a brake disc to the inside and a chain sprocket to the outside of a single-sided swingarm (originally patented by ELF of France), and attached with a single castellated nut and cotter pin.