Castel Nut Fine Thread Black Steel 1/2-20 Grade 2

Secure these nuts by inserting a cotter pin or safety wire through the slots and a drilled hole in your bolt for mild loosening resistance. They're also known as castle nuts and slotted nuts. They’re not recommended for use on parts exposed to high vibration because the pin is prone to shearing under prolonged stress. Height includes the slots. Cotter pins are not included.