Stainless Grades for Fasteners: 304, 316, 410 and the Rest

The grades held

SUS201, 202, 302, 304, 305, 316, 410 and 430.

Austenitic: 302, 304, 305, 316

These are the corrosion performers. 304 and 305 cover general exterior work. 316 adds molybdenum, which is what lets it resist pitting in chloride — sea air, pool halls, roads treated with de-icing salt. In the annealed condition they are non-magnetic, which is why a magnetised nut setter will not pick one up.

Martensitic and ferritic: 410 and 430

Both are magnetic. 410 can be hardened, which is why it appears in self drilling constructions where the point has to cut steel — an austenitic grade cannot be made hard enough to do that on its own.

Property classes

A2-70, A2-80, A4-70 and A4-80. A2 is the chromium-nickel group, broadly 304; A4 is the molybdenum-bearing group, broadly 316. The number is the tensile strength class, so A4-80 is a 316-type steel at the higher of the two strength levels.

Two practical warnings

Austenitic stainless galls if it is run down fast and dry — slow the assembly or lubricate the thread. And stainless is more ductile than a hardened carbon screw, so in hardwood or near an edge it will twist off before it splits its way through; pilot it.

Everything on this page describes the specification range Beyond Industry Groups Limited works to. Where a figure is a laboratory test result rather than a service life, it is described as such.