Heavy hex jam nuts are thinner than a standard heavy hex nut but have the same dimension across the flats and corners. Heavy hex jam nuts have two common applications. A heavy hex jam nut can be threaded onto a bolt and run tight against the standard heavy hex nut which will lock the nut in place and prevent it from backing off. Heavy hex jam nuts are sometimes used for leveling purposes as well. Since hot-dip galvanizing typically adds 2.2 to 5 mils of thickness to the threaded portion of a fastener, galvanized heavy hex jam nuts are tapped oversize to compensate for the corrosion resistant coating on the bolts.