ASME B16.20 — Spiral wound gasket — Class 300
ASME B16.20 Spiral wound gasket — Class 300 — 21 sizes.
| NPS | Inner ring ID (d1) (mm) | Sealing element ID (d2) (mm) | Sealing element OD (d3) (mm) | Centering ring OD (d4) (mm) |
|---|---|---|---|---|
| 1/2 | 14.2 | 19.1 | 31.8 | 54.1 |
| 3/4 | 20.6 | 25.4 | 39.6 | 66.8 |
| 1 | 26.9 | 31.8 | 47.8 | 73.2 |
| 1-1/4 | 38.1 | 47.8 | 60.5 | 82.6 |
| 1-1/2 | 44.5 | 54.1 | 69.9 | 95.3 |
| 2 | 55.6 | 69.9 | 85.9 | 111.3 |
| 2-1/2 | 66.5 | 82.6 | 98.6 | 130.3 |
| 3 | 81 | 101.6 | 120.7 | 149.4 |
| 3-1/2 | — | 114.3 | 133.4 | 165.1 |
| 4 | 106.4 | 127 | 149.4 | 181.1 |
| 4-1/2 | — | 139.7 | 165.1 | 196.9 |
| 5 | 131.8 | 155.7 | 177.8 | 215.9 |
| 6 | 157.2 | 182.6 | 209.6 | 251 |
| 8 | 215.9 | 233.4 | 263.7 | 308.1 |
| 10 | 268.2 | 287.3 | 317.5 | 362 |
| 12 | 317.5 | 339.9 | 374.7 | 422.4 |
| 14 | 349.3 | 371.6 | 406.4 | 485.9 |
| 16 | 400.1 | 422.4 | 463.6 | 539.8 |
| 18 | 449.3 | 474.7 | 527.1 | 596.9 |
| 20 | 500.1 | 525.5 | 577.9 | 654.1 |
| 24 | 603.3 | 628.7 | 685.8 | 774.7 |
- Piping-World and Wermac agree; Wermac omits NPS 3-1/2 and 4-1/2 (those two rows single-source, no inner ring listed).
- NPS 20 d2: Wermac 525.6 vs Piping-World 525.5 mm; Piping-World kept (matches Class 150 value).
- Thickness: inner/centering ring 2.97–3.33 mm, sealing element 4.45 mm (Wermac). For RF flanges to ASME B16.5.
Sources: piping-world.com/spiral-wound-gasket-dimensions-class-300 · wermac.org/gaskets/dim_gaskets_sw300.html