Countersunk Washers (90° Seat) manufactured in A2 Stainless Steel (ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70) are dimensioned to Trade series (90° countersunk washer). The sections below give the mechanical and physical properties of the grade, its behavior in corrosive and elevated-temperature service, and the full size table.
Why Choose A2 Stainless Steel for Countersunk Washers (90° Seat)
The most common stainless group for indoor and general outdoor fasteners. For countersunk washers (90° seat), this matters when good general corrosion resistance is the primary requirement.
Mechanical & Physical Properties
| Grade designation | ISO 3506 group A2 (304 / 1.4301), commonly supplied A2-70 |
|---|---|
| Magnetic response | Largely non-magnetic |
| Service temperature | approx. -200 °C to +400 °C, subject to the property class and the joint |
| Corrosion characteristic | Good general corrosion resistance |
Corrosion Behavior in Service
A2 (304) gives excellent atmospheric and most-water corrosion resistance and is the most common stainless for Countersunk Washers (90° Seat) in indoor and general outdoor service. In chloride-bearing environments (marine air, road salt, swimming pools) consider stepping up to A4 (316).
Comparable Grades
For Countersunk Washers (90° Seat), the alternative stainless grade is A4 (316). 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
Expect the aluminum to corrode, not the fastener — stainless sits higher in the galvanic series, so the aluminum is the one that gives up material. A small fastener in a thick section spreads the loss over a large area and is usually fine; a large fastener in thin sheet concentrates it and is not. Keep water out of the joint, or isolate the two metals with a nylon or coated washer and a sealant.
Sizes of Countersunk Washers (90° Seat) Available in A2 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 |
