Description
ISO 7089 Plain Washer 3×7-A4 — BOLTON SKU 56930.
About the ISO 7089 Plain Washer 3×7-A4
The ISO 7089 Plain Washer 3×7-A4 is a normal-series flat washer for M3 fasteners, made in A4 austenitic stainless steel. ISO 7089 specifies plain washers of product grade A in hardness classes 200 HV and 300 HV; stainless steel washers to this standard are specified at 200 HV. For the M3 size the standard’s dimensions are a 3.2 mm nominal inside diameter, 7 mm nominal outside diameter and 0.5 mm nominal thickness (tolerance bands roughly 3.20–3.38 mm bore, 6.64–7.00 mm OD, 0.45–0.55 mm thickness). The washer spreads the bearing load of an M3 screw or nut over a larger area, protects soft or coated surfaces from marring during tightening, and helps bridge slightly oversized clearance holes. In A4 (316-type) stainless it matches the corrosion class of the A4 screws BOLTON lists in the same family.
Key specifications
| Standard | ISO 7089 (plain washers, normal series, product grade A) |
|---|---|
| Nominal size | M3 |
| Inside diameter | 3.2 mm nominal (3.20–3.38 mm) |
| Outside diameter | 7 mm nominal (6.64–7.00 mm) |
| Thickness | 0.5 mm nominal (0.45–0.55 mm) |
| Hardness class | 200 HV (stainless execution) |
| Material | A4 austenitic stainless steel (316 type, ISO 3506 family) |
Typical applications
This washer is fitted under the heads and nuts of M3 fasteners on electronics enclosures, instrument housings and light brackets to distribute clamping load and protect painted or anodised surfaces. Pairing it with A4 screws keeps the whole joint in one corrosion class for coastal, marine-influenced or washdown installations.
Supplied by BOLTON Technical Equipment Supplies against request for quotation. Add this item to your RFQ basket to request pricing, lead time and documentation requirements (e.g. CoC, datasheets or test reports where applicable).
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