Nuts have internal machine threads, for use with machine thread bolts and screws.
A standard six sided nut.
A hex nut with a nylon ring to resist loosening.
A thinner version of a hex nut.
A long nut used to connect pieces of threaded rod or other male threaded fasteners.
A nut with a finished top that covers the end of the bolt. Bolts must be in the proper length.