A4 Stainless Steel Countersunk Washers (90° Seat) are supplied to our own published dimensions — this is a trade-series article rather than one covered by a dimensional standard, so confirm the figures against the part you are replacing. 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.
Why Choose A4 Stainless Steel for Countersunk Washers (90° Seat)
Specified for marine, coastal and chemical applications. For countersunk washers (90° seat), 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 countersunk washers (90° seat) 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 Countersunk Washers (90° Seat), the alternative stainless grade is A2 (304). Choose A2 (304) for general use and A4 (316) wherever chlorides are present; the molybdenum in A4 is the whole difference. Remember that stainless is the corrosion answer, not the strength answer — for load, look at class 8.8 or 10.9 instead.
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 Countersunk Washers (90° Seat) Available in A4 Stainless Steel
| For screw size | Inner diameter d1 (mm) | Outer diameter d2 (mm) | Thickness t (mm) | Countersink angle | Material | Finish | Note |
|---|---|---|---|---|---|---|---|
| M4 | 4.3 | 11.0 | 2.0 | 90 | Stainless A2 | Passivated | Matches ISO 7046 heads |
| M5 | 5.3 | 13.0 | 2.5 | 90 | Stainless A2 | Passivated | Matches ISO 7046 heads |
| M6 | 6.4 | 16.0 | 3.0 | 90 | Stainless A2 | Passivated | Matches ISO 7046 heads |
| M8 | 8.4 | 20.0 | 3.5 | 90 | Stainless A2 | Passivated | Matches ISO 10642 heads |
| M10 | 10.5 | 24.0 | 4.0 | 90 | Steel | Zinc plated | Matches ISO 10642 heads |
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.
