A2 Stainless Steel Extra-Thick Flat Washers combine the dimensional form of Trade series (heavy-duty thick plain washers) with the material properties of grade ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70: good general corrosion resistance, largely non-magnetic, service range approx. -200 °C to +400 °C, subject to the property class and the joint. This page summarizes the grade data, its corrosion behavior in service, the comparable grades, and the sizes supplied.
Why Choose A2 Stainless Steel for Extra-Thick Flat Washers
The most common stainless group for indoor and general outdoor fasteners. For extra-thick flat washers, this matters when good general corrosion resistance is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70 |
|---|---|
| Magnetic response | Largely non-magnetic |
| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
| Corrosion characteristic | Good general corrosion resistance |
Galvanic & Galling Considerations
For stainless extra-thick flat washers the compatibility question is galvanic rather than galling: joined to aluminum or galvanized steel in wet service, stainless drives corrosion of the less-noble metal. Isolate with a coating, sleeve or non-conductive washer where the joint sees moisture. Note also that stainless is softer than hardened carbon steel, so where the part carries a wear or shear duty, check the load against the grade before substituting.
Comparable Grades
For Extra-Thick Flat Washers, the alternative stainless grade is A4 (316). Choose A2 (304) for general use and A4 (316) wherever chlorides are present; the molybdenum in A4 is the whole difference. Remember that stainless is the corrosion answer, not the strength answer — for load, look at class 8.8 or 10.9 instead.
Using Stainless Fasteners in Aluminum
Stainless steel is more noble than aluminum, so with an electrolyte present — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. Area ratio decides how bad it gets: a small stainless fastener in a large aluminum section is normally acceptable, a large stainless fastener in thin aluminum is not. Where the joint gets wet, isolate the metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.
Sizes of Extra-Thick Flat Washers Available in A2 Stainless Steel
| Bolt size | Material | Relative thickness | Purpose | Finish options |
|---|---|---|---|---|
| M10 | carbon steel or stainless steel | greater than the standard plain washer | reduce local deformation under heavy clamping | zinc plated or plain |
| M12 | carbon steel or stainless steel | greater than the standard plain washer | reduce local deformation under heavy clamping | zinc plated or plain |
| M16 | carbon steel or stainless steel | greater than the standard plain washer | increase bearing area on soft members | zinc plated or plain |
| M20 | carbon steel or stainless steel | greater than the standard plain washer | increase bearing area on soft members | zinc plated or plain |
