slotted nut

slotted nut

[′släd·əd ′nət]
(design engineering)
A regular hexagon nut with slots cut across the flats of the hexagon so that a cotter pin or safety wire can hold it in place.
References in periodicals archive ?
The best method of tightening this slotted nut is to use a wrench that fits over the magazine tube.
A castle nut (also called a castellated nut or slotted nut) with cotter pin is used to secure the wheel hub to the vehicle.