Hex nuts are six sided general purpose fasteners with internal screw threads. The most common are hexagonal fastener with internal threads that screws on to the shank of a bolt or a hex cap screw.
Heavy hex nuts are slightly larger and thicker than standard (finished) hex nuts. There are numerous grades and the heavy pattern is typically used for large diameter and high strength bolts. Since hot dip galvanizing typically adds 2.2 to 5 mils of thickness to the threaded portion of a fastener, galvanized heavy hex nuts are tapped oversize to compensate for the corrosion resistant coating on the bolts.
Hex Machine Nut designed specifically to thread on to small diameter machine screws. These are typically thinner than regular nuts with a finished side for butting up against the surface that does not need a washer. Thinner than a jam nut, this thin hex nut is used on panels or when a low profile is needed. A Hex nut with reversed threads, tightening is done by spinning counter clockwise. Others are Machine Screw Nut, Hex Nut Left hand and Panel Hex Nut.