A4 Stainless Steel (ISO 3506 group A4 (316 / 1.4401), commonly supplied A4-80) is specified for marine, coastal and chemical applications. Specified on bonded sealing washers it determines the corrosion behaviour (superior, including marine and chloride environments) and the service temperature range (approx. -200 °C to +400 °C, subject to the property class and the joint); the dimensions are ours rather than a standard's, and are listed in full below.
Why Choose A4 Stainless Steel for Bonded Sealing Washers
Specified for marine, coastal and chemical applications. For bonded sealing 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 Bonded Sealing Washers in marine, coastal, swimming-pool or food-processing environments, A4 is the default selection.
Galvanic & Galling Considerations
Two important notes for stainless bonded sealing washers: (1) stainless can gall on stainless threads under load — use a thread lubricant or anti-galling compound, especially for M6 and below; (2) when joined to aluminum or galvanized steel, stainless can drive galvanic corrosion of the less-noble metal in wet service — isolate with a coating or sleeve where appropriate.
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 Bonded Sealing Washers Available in A4 Stainless Steel
| Thread size | Inner diameter d1 (mm) | Outer diameter d2 (mm) | Thickness s (mm) | Max temperature (deg C) | Reference standard |
|---|---|---|---|---|---|
| M4 | 4.1 | 8 | 1.0 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M5 | 5.1 | 10 | 1.0 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M6 | 6.1 | 12 | 1.5 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M8 | 8.2 | 14 | 1.5 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M10 | 10.2 | 16 | 1.5 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M12 | 12.2 | 19 | 2.0 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M14 | 14.2 | 21 | 2.0 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M16 | 16.3 | 24 | 2.0 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M18 | 18.3 | 26 | 2.0 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M20 | 20.3 | 28 | 2.0 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M22 | 22.3 | 30 | 2.0 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M24 | 24.3 | 32 | 2.0 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M27 | 27.4 | 36 | 2.5 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M30 | 30.4 | 39 | 2.5 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M33 | 33.5 | 43 | 2.5 | 120 | Trade series (bonded seal washer, Dowty pattern) |
| M36 | 36.5 | 46 | 2.5 | 120 | Trade series (bonded seal washer, Dowty pattern) |
Dimensions are independent of the material: the table above lists the sizes supplied, and on this page every one of them is quoted in A4 Stainless Steel. The catalogue's default material column has been omitted here so it cannot be read as contradicting that.
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.
