Short answer: Fastener grade encodes both material and strength — A2/A4 are the 304/316 stainless property classes, B7 and L7 are alloy-steel bolts for high and low temperature, and carbon-steel grades run 4.8 to 12.9 by proof strength — so the marking on the head tells you exactly what the bolt can do.
At a Glance
Reading the Grade
Stainless fasteners use the A-system: A2 is 304, A4 is 316, and the trailing number (e.g. A2-70) is the property class — roughly 700 MPa minimum tensile. Carbon and alloy bolts use the dot-system where 8.8, 10.9 and 12.9 give tensile and yield directly. Our Fasteners Supplier и Stainless Steel Fasteners Guide stock covers the common classes, and the underlying alloy families are in Градации нержавеющей стали с пояснениями.
Stainless vs Alloy vs Carbon
A2/A4 resist corrosion but are not high-strength; B7 (Cr-Mo) is the high-temperature bolting workhorse and L7 the low-temperature one, both far stronger than stainless. All three can corrode differently in the same plant, so a bolt and flange of unlike metal invite attack — plan with Galvanic Corrosion Guide and protect with How To Prevent Metal Rust. Austenitic stainless bolts also seize without care — see our Stainless Steel Fasteners Guide for grade and anti-seize guidance — and can crack under chloride stress per Stress Corrosion Cracking.
Selecting & Specifying
Specify the grade by service temperature, strength and environment, then control the surface: nitriding or plating for wear follows Nitriding Vs Carburizing, and hardness is verified per Metal Hardness Testing Methods. Fit and preload depend on the tolerance band in Metal Tolerances Fits Guide; for corrosive duty choose A4 or a nickel alloy per Metal Surface Treatment Guide.
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Tell HXSCO your requirements and we will respond with a competitive quote and lead time.
Часто задаваемые вопросы
A2 is the 304 stainless family and 70 is the property class, meaning a minimum tensile strength of about 700 MPa. A4-70 is the 316 equivalent for marine and chemical service.
B7 is a chromium-molybdenum alloy steel for high-temperature bolting (e.g. pressure vessels); L7 is a low-temperature alloy steel for cryogenic and cold service.
A4-70 / A4-80 (316 stainless) is the standard for marine and coastal duty; for extreme corrosion a nickel alloy such as Monel may be specified.
Yes, but lower than alloy steel — A2/A4 tops out around class 80 (800 MPa). For high-strength structural bolting, carbon or alloy steel grades such as 8.8 or 10.9 are used instead.
Yes. HXSCO supplies stainless, alloy and carbon-steel fasteners with grade markings, hardness and mill certificates on request.
Source Graded Fasteners from HXSCO
HXSCO supplies A2/A4 stainless, B7/L7 alloy and carbon-steel fasteners with grade markings and mill certificates. Send your grade, size and quantity for a quote.