Heavy hex bolts are generally specified for high temperature or high pressure applications, particularly where bolt heads will bear against flanges. Standard diameters are 1/2″ and larger. The main difference between a heavy hex bolt and a regular (or finished) hex bolt is the distance across opposite flats of the hex. Heavy hex bolts are 1/8 of an inch larger than a finished hex bolt of the same diameter. The formula for determining hex size is one-and-a-half times the diameter plus 1/8″.
ASTM (ASME) A193 is one specification that is usually sited in connection with heavy hex bolts. Several different materials are covered by ASTM A193. Nickel Systems can supply bolting to A193 B8 (304 Stainless), A193 B8C (347 Stainless), A193 B8M (316 Stainless), A193 B8R (Nitronic® 50), A193 B8S (Nitronic® 60) and A193B8T (321 Stainless), as well as Strain Hardened ASTM A193 B8 Class 2 (304 Stainless) and A193 B8M Class 2 (316 Stainless).
Nickel Systems is not limited to materials covered by ASTM A193. Currently, we have heavy hex bolts in Hastelloy® C276 (Alloy C276) and Carpenter® 20 (Alloy 20) in stock. Bolting in other materials can be provided.