Castle and Slotted Nuts

Used primarily as safety nuts, these nuts are slotted to receive a cotter pin or wire which passes through a drilled hole in the bolt and locks it.

In assembly the nuts are torqued to preload value, then nut position is adjusted to line up the slots with the hole in the bolt. This is a disadvantage in critical-preload applications because of possible alignment variations which may lead to application of too much or too little torque.