A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. When fender washers are specified in this grade, the dimensions remain per DIN 9021; the material determines corrosion behavior (superior, including marine and chloride environments) 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 A4 Stainless Steel for Fender Washers
Specified for marine, coastal and chemical applications. For fender washers, this matters when superior, including marine and chloride environments is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80 |
|---|---|
| Magnetic response | Largely non-magnetic |
| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
| Corrosion characteristic | Superior, including marine and chloride environments |
Galvanic & Galling Considerations
For stainless fender 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 Fender Washers, the alternative stainless grade is A2 (304). 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 Fender Washers Available in A4 Stainless Steel
| For bolt size | Inner diameter d1 min (mm) | Outer diameter d2 max (mm) | Thickness h (mm) | Reference standard | Notes |
|---|---|---|---|---|---|
| M3 | 3.2 | 9.0 | 0.8 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M4 | 4.3 | 12.0 | 1.0 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M5 | 5.3 | 15.0 | 1.2 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M6 | 6.4 | 18.0 | 1.6 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M8 | 8.4 | 24.0 | 2.0 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M10 | 10.5 | 30.0 | 2.5 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M12 | 13.0 | 37.0 | 3.0 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M14 | 15.0 | 44.0 | 3.0 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M16 | 17.0 | 50.0 | 3.0 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M20 | 21.0 | 60.0 | 4.0 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M24 | 25.0 | 72.0 | 5.0 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M30 | 31.0 | 90.0 | 6.0 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
| M36 | 37.0 | 110.0 | 8.0 | DIN 9021 / ISO 7093 | Oversized OD for bearing on soft materials |
