These screws are manufactured with alloy steel, which contains elements to help the screws become more responsive to heat and mechanical treatments.- Grade B7 hex head cap screws with 1/2-13 and larger thread sizes provide an increased bearing surface and thereby qualify as heavy hex bolts. Heavy Hex Bolt Type / Heavy Hex Bolt Head Type - Bolts / Hex Basic Material / Steel Material Grade / Grade B7 Fastener Finish / Plain Dia./Thread Size / 5/8"-11 Fastener Length / 2 1/4 in Fastener Thread Direction / Right Hand Fastener Thread Type / UNC (Coarse) Fastener Industry Standards / ASME B18.2.1 Min. Thread Length / 1 1/2 in Fastener Thread Style / Partially Threaded Head Height / 25/64 in Head Width / 1 1/16 in Tensile Strength / 125,000 psi Rockwell Hardness / C35