A family name covering 302, 303, 304 and 305 stainless, the most common corrosion-resistant fastener material. These grades cannot be hardened by heat treatment, so strength comes from cold work and stays well below alloy steel: metric A2-70 is about 700 MPa tensile against 1,040 MPa for class 10.9. They are non-magnetic or only faintly magnetic and notorious for galling when stainless nuts run onto stainless bolts.
It's 18-8 stainless bolts in 18-8 nuts, so anti-seize every one and turn the impact down or they'll gall solid.
Also heard as
- A2 stainless
- 304 stainless
Related terms
Galling
Adhesive wear where thread surfaces cold-weld and tear under load, seizing a nut partway down a bolt.
Anti-seize
A grease loaded with metal or ceramic particles that stops threads from galling, rusting or bonding under heat.
Passivation
An acid treatment that strips free iron from stainless fasteners and restores their chromium oxide film.
Property class
The metric strength grade of a bolt or nut, stamped on the head as a number such as 8.8, 10.9 or 12.9.