A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. Specified on insulating shoulder washers it determines the corrosion behaviour (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); the dimensions are ours rather than a standard's, and are listed in full below.
Why Choose A4 Stainless Steel for Insulating Shoulder Washers
Specified for marine, coastal and chemical applications. For insulating shoulder 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 |
Corrosion Behavior in Service
A4 (316) adds 2–3% molybdenum to the A2 (304) composition, which dramatically improves resistance to chloride-pitting corrosion. For Insulating Shoulder Washers in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Galvanic & Galling Considerations
For stainless insulating shoulder 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.
Using Stainless Fasteners in Aluminum
The galvanic couple here runs the wrong way: aluminum is the less noble metal, so it corrodes and the fastener does not. What governs the rate is the ratio of areas — a large anode and a small cathode is a tolerable combination, the reverse concentrates the attack into thin material around the hole. An isolating washer plus sealant breaks the circuit; where that is impractical, match the fastener to the substrate.
Sizes of Insulating Shoulder Washers Available in A4 Stainless Steel
| Screw size | Bore d1 (mm) | Shoulder outer diameter (mm) | Flange outer diameter d2 (mm) | Shoulder length (mm) | Flange thickness (mm) | Reference standard |
|---|---|---|---|---|---|---|
| M2.5 | 2.7 | 3.6 | 6.0 | 1.5 | 0.8 | Industry standard |
| M3 | 3.2 | 4.2 | 7.0 | 1.5 | 0.8 | Industry standard |
| M3 | 3.2 | 4.2 | 7.0 | 3.0 | 0.8 | Industry standard |
| M4 | 4.3 | 5.4 | 9.0 | 2.0 | 1.0 | Industry standard |
| M4 | 4.3 | 5.4 | 9.0 | 3.5 | 1.0 | Industry standard |
| M5 | 5.3 | 6.6 | 11.0 | 2.5 | 1.0 | Industry standard |
| M6 | 6.4 | 7.8 | 13.0 | 3.0 | 1.2 | Industry standard |
Dimensions are independent of the material: the table above lists the sizes supplied, and on this page every one of them is quoted in A4 Stainless Steel. The catalogue's default material column has been omitted here so it cannot be read as contradicting that.
Custom manufacturing · Made to drawing
Need this washer in a grade that is not listed?
A4 Stainless Steel is one of the grades the catalog describes. Bearing area is usually the reason for a special washer: a larger outside diameter to spread load into a softer material, or a thicker section to resist dishing. Made by stamping or punching.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
