ASME B16.21 — Non-metallic flat ring gasket — Class 300
ASME B16.21 Non-metallic flat ring gasket — Class 300 — 20 sizes.
| NPS | Gasket ID (mm) | Gasket OD (mm) |
|---|---|---|
| 1/2 | 21.3 | 53.8 |
| 3/4 | 26.9 | 66.5 |
| 1 | 33.3 | 73.2 |
| 1-1/4 | 42.2 | 82.5 |
| 1-1/2 | 48.5 | 95.2 |
| 2 | 60.5 | 111.3 |
| 2-1/2 | 73.2 | 130 |
| 3 | 88.9 | 149.4 |
| 3-1/2 | 101.6 | 165.1 |
| 4 | 114.3 | 180.8 |
| 5 | 141.2 | 215.9 |
| 6 | 168.1 | 251 |
| 8 | 218.9 | 307.8 |
| 10 | 273.1 | 361.9 |
| 12 | 323.8 | 422.1 |
| 14 | 355.6 | 485.6 |
| 16 | 406.4 | 539.8 |
| 18 | 457.2 | 596.9 |
| 20 | 508 | 654 |
| 24 | 609.6 | 774.7 |
- Values from flangeboltchart.com (ASME B16.21-2021 Tables 4.1-4/4.1-5, inches) converted to mm at 25.4.
- Cross-checked: J.A. Harrison mm tables (e.g. NPS 1/2 ID 21.4, OD 47.6 / 54.0 mm) and Piping-World/Wermac rounded-mm tables (e.g. NPS 6: 168/222/251; NPS 12: 324/410/422; NPS 24: 610/718/775) agree after rounding.
- Wermac OD tolerance: +0/−1.5 mm NPS 12 and smaller, +0/−3.0 mm NPS 14 and larger.
- For RF flanges to ASME B16.5. NPS 22 not listed in sources.
Sources: flangeboltchart.com/gasket/dimensions/non-metallic · jaharrison.co.uk/product-specifications/gasket-dimensions/as · jaharrison.co.uk/product-specifications/gasket-dimensions/as · piping-world.com/dimension-of-flat-ring-gaskets-up-to-24-inc · wermac.org/gaskets/dim_gaskets_fl.html