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 spherical washers & conical seats are specified in this grade, the dimensions remain per DIN 6319; 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 Spherical Washers & Conical Seats
The most common stainless group for indoor and general outdoor fasteners. For spherical washers & conical seats, 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 spherical washers & conical seats 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 Spherical Washers & Conical Seats, 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 Spherical Washers & Conical Seats Available in A2 Stainless Steel
| Bolt size | Bore d1 (mm) | Outer diameter d2 (mm) | Height h Form C (mm) | Thickness s (mm) | Conical seat height Form D (mm) | Spherical radius R (mm) | Max misalignment | Reference standard |
|---|---|---|---|---|---|---|---|---|
| M5 | 5.5 | 12 | 3.5 | 3.5 | 3.0 | 9 | 3 deg | DIN 6319 C/D |
| M6 | 6.4 | 14 | 3.5 | 3.5 | 3.0 | 10.5 | 3 deg | DIN 6319 C/D |
| M8 | 8.4 | 17 | 4.5 | 4.5 | 3.5 | 12.5 | 3 deg | DIN 6319 C/D |
| M10 | 10.5 | 21 | 5.0 | 5.0 | 4.0 | 15.5 | 3 deg | DIN 6319 C/D |
| M12 | 13 | 24 | 6.0 | 6.0 | 5.0 | 17.5 | 3 deg | DIN 6319 C/D |
| M14 | 15 | 28 | 7.0 | 7.0 | 5.5 | 20.5 | 3 deg | DIN 6319 C/D |
| M16 | 17 | 30 | 7.0 | 7.0 | 6.0 | 22 | 3 deg | DIN 6319 C/D |
| M20 | 21 | 36 | 8.5 | 8.5 | 7.0 | 26.5 | 3 deg | DIN 6319 C/D |
| M24 | 25 | 44 | 10 | 10 | 8.0 | 32 | 3 deg | DIN 6319 C/D |
| M30 | 31 | 56 | 12 | 12 | 10 | 40 | 3 deg | DIN 6319 C/D |
