ASTM A193 Grade B7 heavy hex head bolts are high strength fasteners manufactured from heat treated alloy steel AISI 4140/4142, quenched and tempered. Dimensional specifications are governed by ASME B18.2.1. Grade markings consists of both the grade symbol "B7" and the manufacturer's identification mark. Inch series fasteners meeting ASTM A193 Grade B7 specifications are typically used in flange bolting applications. ASTM A193 covers the requirements for high temperature and high pressure bolting. Heavy hex head bolts have a larger head to increase the bearing surface and distribute the clamping load over a larger area. Bolts listed that are smaller than 1/2" diameter may be finished pattern bolts. A193 B7 hex bolts, as well as all thread stud bolts having diameters above 1" are most common 8UN (8 threads per inch) and are also available UNC (coarse thread).