Material page for cup washers in A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80). The sizes below are the ones we supply; there is no published dimensional standard for this article, so the table rather than a standard number is what to quote. Corrosion behaviour is superior, including marine and chloride environments and the service range is approx. -200 °C to +400 °C, subject to the property class and the joint.
Why Choose A4 Stainless Steel for Cup Washers
Specified for marine, coastal and chemical applications. For cup 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 Cup Washers in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Comparable Grades
For Cup Washers, 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 Cup Washers Available in A4 Stainless Steel
| Screw size | Inner diameter d1 (mm) | Outer diameter d2 (mm) | Thickness s (mm) | Cup depth (mm) | Seat angle (deg) | Reference standard |
|---|---|---|---|---|---|---|
| No.6 (3.5 mm) | 3.7 | 10.0 | 0.6 | 1.6 | 90 | Industry standard |
| No.8 (4.0 mm) | 4.2 | 11.5 | 0.7 | 1.8 | 90 | Industry standard |
| No.10 (4.8 mm) | 5.0 | 13.0 | 0.8 | 2.0 | 90 | Industry standard |
| No.12 (5.5 mm) | 5.7 | 15.0 | 0.9 | 2.3 | 90 | Industry standard |
| M4 | 4.3 | 11.5 | 0.7 | 1.8 | 90 | Industry standard |
| M5 | 5.3 | 13.0 | 0.8 | 2.0 | 90 | Industry standard |
| M6 | 6.4 | 15.0 | 1.0 | 2.4 | 90 | Industry standard |
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.
