A4 Stainless Steel Flat Washers combine the dimensional form of ISO 7089 / ISO 7093 with the material properties of grade ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80: superior, including marine and chloride environments, largely non-magnetic, service range approx. -200 °C to +400 °C, subject to the property class and the joint. This page summarizes the grade data, its corrosion behavior in service, the comparable grades, and the sizes supplied.
Why Choose A4 Stainless Steel for Flat Washers
Specified for marine, coastal and chemical applications. For flat 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 flat 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 Flat Washers, the alternative stainless grade is A2 (304). A2 (304) covers general indoor and outdoor service. A4 (316) adds molybdenum, which is what buys the chloride resistance for marine and de-icing-salt exposure. Where strength matters more than corrosion, plated alloy steel in class 8.8 or 10.9 is the swap to make.
Using Stainless Fasteners in Aluminum
Stainless steel is more noble than aluminum, so with an electrolyte present — rain, condensation, salt spray — the aluminum becomes the anode and corrodes at the joint. Area ratio decides how bad it gets: a small stainless fastener in a large aluminum section is normally acceptable, a large stainless fastener in thin aluminum is not. Where the joint gets wet, isolate the metals with a coated or nylon washer and a sealant, or specify an aluminum or coated fastener instead.
Sizes of Flat Washers Available in A4 Stainless Steel
| For bolt size | Inner diameter d1 min (mm) | Outer diameter d2 max (mm) | Thickness h (mm) | Reference standard |
|---|---|---|---|---|
| M1.6 | 1.7 | 4.0 | 0.3 | ISO 7089 |
| M2 | 2.2 | 5.0 | 0.3 | ISO 7089 |
| M2.5 | 2.7 | 6.0 | 0.5 | ISO 7089 |
| M3 | 3.2 | 7.0 | 0.5 | ISO 7089 |
| M3.5 | 3.7 | 8.0 | 0.5 | ISO 7089 |
| M4 | 4.3 | 9.0 | 0.8 | ISO 7089 |
| M5 | 5.3 | 10.0 | 1.0 | ISO 7089 |
| M6 | 6.4 | 12.0 | 1.6 | ISO 7089 |
| M7 | 7.4 | 14.0 | 1.6 | ISO 7089 |
| M8 | 8.4 | 16.0 | 1.6 | ISO 7089 |
| M10 | 10.5 | 20.0 | 2.0 | ISO 7089 |
| M12 | 13.0 | 24.0 | 2.5 | ISO 7089 |
| M14 | 15.0 | 28.0 | 2.5 | ISO 7089 |
| M16 | 17.0 | 30.0 | 3.0 | ISO 7089 |
| M18 | 19.0 | 34.0 | 3.0 | ISO 7089 |
| M20 | 21.0 | 37.0 | 3.0 | ISO 7089 |
| M22 | 23.0 | 39.0 | 3.0 | ISO 7089 |
| M24 | 25.0 | 44.0 | 4.0 | ISO 7089 |
| M27 | 28.0 | 50.0 | 4.0 | ISO 7089 |
| M30 | 31.0 | 56.0 | 4.0 | ISO 7089 |
| M33 | 34.0 | 60.0 | 5.0 | ISO 7089 |
| M36 | 37.0 | 66.0 | 5.0 | ISO 7089 |
| M39 | 40.0 | 72.0 | 6.0 | ISO 7089 |
| M42 | 43.0 | 78.0 | 7.0 | ISO 7089 |
| M45 | 46.0 | 85.0 | 7.0 | ISO 7089 |
| M48 | 50.0 | 92.0 | 8.0 | ISO 7089 |
| M52 | 54.0 | 98.0 | 8.0 | ISO 7089 |
| M56 | 58.0 | 105.0 | 9.0 | ISO 7089 |
| M60 | 62.0 | 110.0 | 9.0 | ISO 7089 |
| M64 | 66.0 | 115.0 | 9.0 | ISO 7089 |
Dimensions are independent of the material: every size above is available in A4 Stainless Steel.
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. Bore, outside diameter, thickness, temper and finish are the variables here — there is no thread to specify, so the fit and the bearing area are what the drawing has to pin down. Made by stamping or punching.
Minimum order from 2,000 pieces; samples within 7 days of drawing approval.
