Heavy Hex Nuts
A six sided internally threaded fastener, which is both thicker and wider than a same-sized finished nut. Nuts size 7/16 and smaller shall be double chamfered. Larger sizes are either double chamfered or chamfered on top with a washer faced bearing surface.
The strongest of all comparably graded nuts because of its greater length of thread engagement and greater resistance to dilation (widening or stretching). Grade-A nuts are used with low carbon heavy hex bolts. Grade-C nuts are recommended for use with A-325 structural bolts. Grade-2H nuts are recommended for use with bolts in high-pressure and high-temperature applications.