Looking up definitions of "castle nut" and "slotted nut" I read they are made to accommodate cotter pins. The nut I am asking about has slits much too small to fit a cotter pin. What is it called and why the slits? Thank you.
It's called a "Slotted Nut". Safety wire can be used in lieu of pin. Some have slots in the nut for the purpose of a lock nut application, where torque must be applied.
