Slotted Hex Nuts

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Slotted nuts, similar in function to castle nuts, are internally threaded, hexagonal nuts with slots cut in the center of the flats.

The slots accommodate a cotter pin or safety wire when installed with a drilled fastener.

A castle nut, also called a castellated nut, or slotted nut, is a nut with slots (notches) cut into one end. The name comes from the nut looking like a medieval castle. The bolt or axle has one or two holes drilled through its threaded end.