Heavy Hex Bolts, (A 320) An alloy or stainless steel hex bolt with a wider head than that of a standard hex machine bolt, manufactured in accordance with ASTM Standard A320. Hex bolts (six sided heads) are the industry standard for fasteners with forged heads. ASTM A307 grade A bolts, all SAE hex bolts, and several other common specifications require a standard (finished) hex head. For specifications such as A307 grade B, A325 and A490 that require a heavy hex pattern, refer to dimensional tolerances for heavy hex bolts or structural bolts. Stainless Steels Material Grade : 304, 304B, 309, 310, 316, 316B, 317, 317L, 321, 347, 401, 416, 430 & 501.