Jam Nuts
Jam nuts are a six-sided internally threaded fastener which is only 2/3 the thickness of a full form nut. Heavy hex jam nuts are a six-sided internally threaded fastener which is only 2/3 the thickness of a heavy hex nut. The thinner pattern is sometimes used as a second nut to 'jam' another nut in place preventing loosening or when a low profile is needed.