BS 4320 Metric Plain Washers — Form A
BS 4320 covers metal washers for general engineering purposes in the metric series. This reference shows the bright normal-diameter Form A washer.
Selected BS 4320 Form A dimensions
| Bolt size | Bore d (min–max mm) | Outside diameter dc (min–max mm) | Thickness h (min–max mm) |
|---|---|---|---|
| M3 | 3.2–3.4 | 6.7–7.0 | 0.4–0.6 |
| M4 | 4.3–4.5 | 8.7–9.0 | 0.7–0.9 |
| M5 | 5.3–5.5 | 9.7–10.0 | 0.9–1.1 |
| M6 | 6.4–6.7 | 12.1–12.5 | 1.4–1.8 |
| M8 | 8.4–8.7 | 16.6–17.0 | 1.4–1.8 |
| M10 | 10.5–10.9 | 20.5–21.0 | 1.8–2.2 |
| M12 | 13.0–13.4 | 23.5–24.0 | 2.3–2.7 |
| M16 | 17.0–17.4 | 29.5–30.0 | 2.7–3.3 |
| M20 | 21.0–21.5 | 36.2–37.0 | 2.7–3.3 |
| M24 | 25.0–25.5 | 43.2–44.0 | 3.7–4.3 |
Reference note: Selected Form A dimensions in millimetres; other forms and sizes are covered by the full schedule. BSI lists BS 4320:1968 as withdrawn (28 June 2021), so check the specified contractual edition before ordering.