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. Material / Carbon Steel Finish / Plain Thread Size / 13 Thread Type / UNC (Coarse) Thread Direction / Right Hand Fastener Length / 4 in Thread Style / Partially Threaded Head Width / 7/8 in Head Height / 5/16 in Tensile Strength / 125,000 psi Rockwell Hardness / C35 System of Measurement / Inch Type / Medium Strength