HILLMAN 880505 Jam Nut, Standard, Fine Thread, 1/2-20 Thread, Steel, Zinc-Plated

A jam nut is low profile, and half as tall as a standard nut. It's often used as a type of locknut where it is jammed up against a standard nut to lock the two in place. Perfect for general applications, you can also use it where a standard nut would not fit. Zinc-plated for moderate corrosion resistance.