ASME B16.20 Class 150 spiral wound gasket dimensions for ASME B16.5 raised-face flanges, NPS 1/2 through NPS 24: inner-ring inside diameter (d1), sealing element (winding) inside diameter (d2), sealing element (winding) outside diameter (d3) and centering (outer) ring outside diameter (d4), all in millimetres. The gasket matches the ASME B16.5 Class 150 flange it seats in; the Class 300 gasket of the same NPS differs because its flange has a larger bolt circle. Values cross-checked across three independent reference tables — Wermac and GlobalSupplyLine agree on all four diameters for every NPS, and FlangeBoltChart confirms the winding inside diameter.
A spiral wound gasket seals between two raised-face flanges. ASME B16.20 sets its dimensions so that the gasket matches the ASME B16.5 flange it seats in. A typical Class 150 gasket has three parts: a solid metal inner ring that locates the inner edge of the winding and resists inward buckling; the spiral winding itself (alternating metal strip and filler) which does the sealing; and a solid metal centering (outer) ring that locates the gasket inside the flange bolts and acts as a compression stop. The four diameters below define those parts. The values are ASME B16.20 Class 150, cross-checked across three independent reference tables.
| NPS | Inner ring ID d1 (mm) | Winding ID d2 (mm) | Winding OD d3 (mm) | Centering ring OD d4 (mm) |
|---|---|---|---|---|
| NPS 1/2 | 14.2 | 19.1 | 31.8 | 47.8 |
| NPS 3/4 | 20.6 | 25.4 | 39.6 | 57.2 |
| NPS 1 | 26.9 | 31.8 | 47.8 | 66.8 |
| NPS 1 1/4 | 38.1 | 47.8 | 60.5 | 76.2 |
| NPS 1 1/2 | 44.5 | 54.1 | 69.9 | 85.9 |
| NPS 2 | 55.6 | 69.9 | 85.9 | 104.9 |
| NPS 2 1/2 | 66.5 | 82.6 | 98.6 | 124.0 |
| NPS 3 | 81.0 | 101.6 | 120.7 | 136.7 |
| NPS 4 | 106.4 | 127.0 | 149.4 | 174.8 |
| NPS 5 | 131.8 | 155.7 | 177.8 | 196.9 |
| NPS 6 | 157.2 | 182.6 | 209.6 | 222.3 |
| NPS 8 | 215.9 | 233.4 | 263.7 | 279.4 |
| NPS 10 | 268.2 | 287.3 | 317.5 | 339.9 |
| NPS 12 | 317.5 | 339.9 | 374.7 | 409.7 |
| NPS 14 | 349.3 | 371.6 | 406.4 | 450.9 |
| NPS 16 | 400.1 | 422.4 | 463.6 | 514.4 |
| NPS 18 | 449.3 | 474.7 | 527.1 | 549.4 |
| NPS 20 | 500.1 | 525.5 | 577.9 | 606.6 |
| NPS 24 | 603.3 | 628.7 | 685.8 | 717.6 |
d1 is the inside diameter of the inner ring (the inner edge of the gasket bore); d2 is the inside diameter of the sealing element, where the spiral winding begins; d3 is the outside diameter of the sealing element, where the winding ends; d4 is the outside diameter of the centering ring, which seats the gasket against the flange bolts. The centering ring outside diameter d4 sits inside the flange bolt circle, so it follows the matching ASME B16.5 Class 150 flange. The Wermac and GlobalSupplyLine tables agree on all four diameters for every NPS; FlangeBoltChart independently confirms the winding inside diameter d2 (0.75 in = 19.1 mm at NPS 1/2, 24.75 in = 628.7 mm at NPS 24).
Gasket thickness, winding metal and filler material are not tabled here: they are selected for the service (typically a 4.5 mm nominal gasket with a 316 stainless winding and a flexible graphite or PTFE filler for Class 150) and do not change the four diameters above. Confirm the winding metal, filler, inner-ring metal and centering-ring metal against the service before ordering.
A spiral wound gasket matches a flange only when the standard, NPS, pressure class and facing all agree, so confirm all four before ordering. The dimensions above are the Class 150 gasket for an ASME B16.5 raised-face flange; a Class 300 gasket of the same NPS has a different centering ring outside diameter because the Class 300 flange has a larger bolt circle. The gasket is not interchangeable between classes even at the same NPS. Match the gasket bore to the flange bore and the centering ring to the flange bolts, fit the full set, and compress the joint evenly so the centering ring seats and the winding is not crushed.
Dimensions are nominal ASME B16.20 Class 150 values and provided for identification and cross-reference. Confirm against the controlling standard and the specific gasket maker’s current data sheet before manufacture or procurement.