18-8 vs. ASTM F593
STAINLESS STEEL HEX HEAD BOLTS AND CAP SCREWS
Stainless Steel, as it applies to fasteners, can be very confusing. 18-8, 304, F593… the differences can be slight, or significant.
18-8 is a term often used to specify fasteners. In reality, 18-8 stainless steel encompasses many different grades of stainless including 302, 302HQ, 303, 303Se, 304, 304L, 305, and 384. 18-8 is actually a reference to the chemical makeup of the stainless steel. In order to be included in the 18-8 family of stainless, there must be 18% Chromium and 8% Nickel present in material’s chemical makeup. But the different grades of stainless that are considered 18-8, can vary greatly due to other elements of there composition. In many applications, requesting 18-8 stainless steel is sufficient. But, if 304 is needed, 304 should be requested. While all 304 stainless is considered 18-8, not all 18-8 stainless is equivalent to 304.
ASTM F593 is a specification for stainless steel bolts, cap screws, and studs. It more stringently specifies material strengths and chemical compositions for multiple classes of stainless steel . The tensile strengths are generally higher than 304 and 316 commercial grades, and at the same time, have tighter limitations. Diameters ranging from 1/4″ through 1-1/2″ are covered under this standard.