castle nut

Etymology
The projections resemble the turrets of a castle.

Noun

 * 1) A nut with rounded extensions projecting past the nut's opening. A cotter pin is inserted through a hole in the bolt and bent around the castle nut's projections to lock the nut in place.

Translations

 * Danish: kronemøtrik
 * Finnish: kruunumutteri
 * Manx: cro cashtal