Spring lock washers come in three thickness grades for the same thread size: No. 1 is the thinnest, No. 2 is for general use and No. 3 is for heavy duty. All three have the same inner diameter; they differ in wire cross-section (width b × thickness t) and outer diameter, so when matching an old part, measuring the thickness t is the easiest way to tell which number it is. The metric No. 2 (M2-M39) and No. 3 (M6-M27) are the No. 2 (general use) and No. 3 (heavy duty) of JIS B 1251, with the same cross-section and maximum outer diameter values.
Most of SFP's stock spring lock washers are No. 1 (the green columns in the table below); only items marked "No. 2" in the product name are No. 2. If you need No. 2 or No. 3 specifically, please state it in your inquiry.
| For screw | ID d | No. 1 (our main stock) | No. 2 | No. 3 | |||
|---|---|---|---|---|---|---|---|
| Width b × thickness t | Max OD D | Width b × thickness t | Max OD D | Width b × thickness t | Max OD D | ||
| M2 | 2.1 (+0.25/0) | 0.8 × 0.4 | 4.1 | 0.9 × 0.5 | 4.4 | 1 × 0.6 | 4.6 |
| M2.5 | 2.6 (+0.3/0) | 0.9 × 0.5 | 5.1 | 1 × 0.6 | 5.2 | 1.2 × 0.8 | 5.7 |
| M3 | 3.1 (+0.3/0) | 1 × 0.6 | 5.7 | 1.1 × 0.7 | 5.9 | 1.3 × 0.9 | 6.3 |
| M3.5 | 3.6 (+0.3/0) | 1 × 0.6 | 6.2 | 1.2 × 0.8 | 6.6 | 1.4 × 1 | 7 |
| M4 | 4.1 (+0.4/0) | 1.1 × 0.7 | 7.3 | 1.4 × 1 | 7.6 | 1.6 × 1.2 | 8.1 |
| M4.5 | 4.6 (+0.4/0) | 1.3 × 0.9 | 8 | 1.5 × 1.2 | 8.3 | 1.7 × 1.4 | 8.8 |
| M5 | 5.1 (+0.4/0) | 1.5 × 1 | 8.9 | 1.7 × 1.3 | 9.2 | 1.9 × 1.5 | 9.7 |
| M6 | 6.1 (+0.4/0) | 2.3 × 1.4 | — | 2.7 × 1.5 | 12.2 | 2.7 × 1.9 | 12.2 |
| 1/4" | 6.5 (+0.4/0) | — | — | 2.8 × 1.6 | 12.5 | 2.8 × 2 | 12.5 |
| M7 | 7.1 (+0.4/0) | — | — | 2.8 × 1.6 | 13.4 | 2.8 × 2 | 13.4 |
| M8 / 5/16" | 8.2 (+0.5/0) | 3 × 1.4 | 15 | 3.2 × 2 | 15.4 | 3.3 × 2.5 | 15.6 |
| 3/8" | 9.8 (+0.5/0) | 3.5 × 1.8 | 17.6 | 3.6 × 2.4 | 17.8 | 3.7 × 2.9 | 18.2 |
| M10 | 10.2 (+0.5/0) | 3.6 × 1.9 | 18.3 | 3.7 × 2.5 | 18.4 | 3.9 × 3 | 18.8 |
| 7/16" | 11.4 (+0.5/0) | 3.9 × 2.2 | 20 | 4 × 2.8 | 20.2 | 4.1 × 3.4 | 20.4 |
| M12 | 12.2 (+0.6/0) | 4.1 × 2.4 | 21.4 | 4.2 × 3 | 21.5 | 4.4 × 3.6 | 21.9 |
| 1/2" | 13 (+0.6/0) | 4.3 × 2.5 | 22.5 | 4.4 × 3.2 | 22.7 | 4.5 × 3.8 | 22.9 |
| M14 / 9/16" | 14.2 (+0.6/0) | 4.6 × 2.8 | 24.5 | 4.7 × 3.5 | 24.5 | 4.8 × 4.2 | 24.7 |
| M16 / 5/8" | 16.2 (+0.8/0) | 5.1 × 3.2 | 28 | 5.2 × 4 | 28 | 5.3 × 4.8 | 28.2 |
| M18 | 18.2 (+0.8/0) | 5.6 × 3.7 | 31 | 5.7 × 4.6 | 31 | 5.9 × 5.4 | 31.4 |
| 3/4" | 19.5 (+0.8/0) | 5.9 × 3.9 | 32.7 | 5.9 × 4.8 | 32.7 | 6.2 × 5.7 | 33.3 |
| M20 | 20.2 (+0.8/0) | 6.1 × 4.1 | 33.8 | 6.1 × 5.1 | 33.8 | 6.4 × 6 | 34.4 |
| M22 / 7/8" | 22.8 (+1/0) | 6.7 × 4.6 | 37.7 | 6.8 × 5.6 | 37.7 | 7.1 × 6.8 | 38.3 |
| M24 | 24.5 (+1/0) | 7 × 4.9 | 40.2 | 7.1 × 5.9 | 40.3 | 7.6 × 7.2 | 41.3 |
| 1" | 26 (+1/0) | 7.3 × 5.1 | 42.4 | 7.5 × 6.4 | 42.8 | 8.1 × 7.3 | 44 |
| M27 | 27.7 (+1.2/0) | 7.7 × 5.4 | 45.1 | 7.9 × 6.8 | 45.3 | 8.6 × 8.3 | 46.7 |
| 1-1/8" | 29.3 (+1.2/0) | 8 × 5.7 | 47.3 | 8.3 × 7.1 | 47.9 | — | — |
| M30 | 30.5 (+1.2/0) | 8.2 × 6 | 49.1 | 8.7 × 7.5 | 49.9 | — | — |
| M32 / 1-1/4" | 32.5 (+1.2/0) | 8.5 × 6.4 | 51.5 | 9.1 × 7.9 | 52.7 | — | — |
| M33 | 33.5 (+1.4/0) | 8.7 × 6.6 | 53.4 | 9.5 × 8.2 | 54.7 | — | — |
| 1-3/8" | 35.8 (+1.4/0) | 9 × 6.7 | 56 | 9.9 × 8.7 | 57.8 | — | — |
| M36 | 36.5 (+1.4/0) | 9.2 × 6.9 | 57.5 | 10.2 × 9 | 59.1 | — | — |
| 1-1/2" | 39 (+1.4/0) | 9.5 × 7.2 | 60.2 | 10.7 × 9.5 | 62.6 | — | — |
| M39 | 39.5 (+1.4/0) | — | — | 10.7 × 9.5 | 63.1 | — | — |
The inner diameter d is the basic size, and its tolerance is plus only (in brackets); D is the maximum outer diameter (including the upper tolerance). The actual outer diameter is about "inner diameter + 2 × width b", usually 0.5-1.5 mm smaller than the D in the table. "—" means that number has no such size. The section width b and thickness t are specification minimums; actual parts are slightly thicker. In JIS B 1251 the inner diameters of M22 and M27 are 22.5 and 27.5. The actual No. 1 for M6 is about ID 6.2 × OD 10.4 × thickness 1.4. The table gives specification reference values and actual parts have manufacturing tolerances; where a counterbore or space is tight, go by the dimensions on the product page or call us to confirm the actual part.
(1) Start from the thread size of the mating screw (for M10, look at the M10 row); (2) measure the thickness t with a caliper and compare with the three columns to determine the number; (3) where there is a counterbore or nearby interference, use the maximum OD D to confirm it will fit. For spring lock washers for inch screws, look at the inch rows (1/4", 3/8"…).
Click a size to open its product page (price and stock status); lists update automatically with our stock.