A4 Stainless Steel Insulating Shoulder Washers are supplied to Industry standard. The grade provides superior, including marine and chloride environments and is largely non-magnetic; the practical service range is approx. -200 °C to +400 °C, subject to the property class and the joint. Property data, grade comparison and the full size table follow.
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
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 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) | Material | Reference standard |
|---|---|---|---|---|---|---|---|
| M2.5 | 2.7 | 3.6 | 6.0 | 1.5 | 0.8 | Nylon 6/6 | Industry standard |
| M3 | 3.2 | 4.2 | 7.0 | 1.5 | 0.8 | Nylon 6/6 | Industry standard |
| M3 | 3.2 | 4.2 | 7.0 | 3.0 | 0.8 | Nylon 6/6 | Industry standard |
| M4 | 4.3 | 5.4 | 9.0 | 2.0 | 1.0 | Nylon 6/6 | Industry standard |
| M4 | 4.3 | 5.4 | 9.0 | 3.5 | 1.0 | Nylon 6/6 | Industry standard |
| M5 | 5.3 | 6.6 | 11.0 | 2.5 | 1.0 | Nylon 6/6 | Industry standard |
| M6 | 6.4 | 7.8 | 13.0 | 3.0 | 1.2 | Nylon 6/6 | Industry standard |
