1/2"-13 Hex Jam Nuts, Steel, Plain - 1800 Pcs - Heavy Duty Fasteners for Construction, Machinery & Automotive Applications

A six-sided internally threaded fastener which is only 2/3 the thickness of a full form nut

Jam nuts are tightened against the work surface and a finished or heavy hex nut is tightened agianst the jam to keep it from loosening