A2 Stainless Steel (ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70) is the most common stainless group for indoor and general outdoor fasteners. When aluminum flat sealing washers are specified in this grade, the dimensions remain per DIN 7603 Type A; the material determines corrosion behavior (good general corrosion resistance) and the service temperature range (approx. -200 °C to +400 °C, subject to the property class and the joint). Both are covered below with the size table.
Why Choose A2 Stainless Steel for Aluminum Flat Sealing Washers
The most common stainless group for indoor and general outdoor fasteners. For aluminum flat sealing 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 aluminum flat sealing 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 Aluminum Flat Sealing Washers, the alternative stainless grade is A4 (316). A2 (304) suits general indoor and outdoor service; A4 (316) adds molybdenum for marine and chloride environments. Where higher strength matters more than corrosion, switch to plated alloy-steel class 8.8 or 10.9.
Using Stainless Fasteners in Aluminum
Stainless steel is more noble than aluminum, so in the presence of an electrolyte — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. The effect is driven by the area ratio: a small stainless fastener in a large aluminum section is normally acceptable, while a large stainless fastener in thin aluminum is not. Where the joint is wet, isolate the two metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.
Sizes of Aluminum Flat Sealing Washers Available in A2 Stainless Steel
| For bolt size | Pitch (mm) | Inside diameter (mm) | Outside diameter (mm) | Thickness options (mm) | Material | Reference standard |
|---|---|---|---|---|---|---|
| M8 | 1.0 | 8.2 | 11.4 | 1.0 / 1.5 / 2.0 | aluminum | DIN 7603 Type A |
| M10 | 1.0 | 10.2 | 13.4 | 1.0 / 1.5 / 2.0 | aluminum | DIN 7603 Type A |
| M12 | 1.5 | 12.2 | 15.9 | 1.0 / 1.5 / 2.0 | aluminum | DIN 7603 Type A |
| M14 | 1.5 | 14.2 | 17.9 | 1.0 / 1.5 / 2.0 | aluminum | DIN 7603 Type A |
| M16 | 1.5 | 16.2 | 19.9 | 1.0 / 1.5 / 2.0 | aluminum | DIN 7603 Type A |
| M20 | 1.5 | 20.2 | 23.9 | 1.0 / 1.5 / 2.0 | aluminum | DIN 7603 Type A |
| M30 | 1.5 | 30.3 | 35.9 | 1.0 / 1.5 / 2.0 | aluminum | DIN 7603 Type A |
| M48 | 2.0 | 48.3 | 54.9 | 1.0 / 1.5 / 2.0 | aluminum | DIN 7603 Type A |
