ASME B16.5 Class 150 flange dimensions: flange outside diameter O, bolt-circle diameter, number of bolts, bolt-hole size and bolt size for raised-face weld-neck flanges from NPS 1/2 through NPS 24. The inch / NPS counterpart to the EN 1092-1 PN references. Includes NPS 2 (6.00 in OD, 4 x 5/8 in), NPS 4 (7.50 in bolt circle, 8 x 5/8 in) and NPS 6 (8 x 3/4 in). Values cross-checked across two independent reference tables.
Class 150 (also written 150 lb or 150#) is the lowest ASME B16.5 pressure class and the most common rating for general piping in the inch / NPS world, the ASME counterpart to the EN 1092-1 PN ratings. The class and NPS fix the bolt pattern, so a Class 150 NPS 4 flange from any maker shares the same 9.00 in outside diameter, 7.50 in bolt circle and eight 5/8 in bolts. The values below are the ASME B16.5 nominal dimensions for the raised-face weld-neck flange across the common NPS 1/2 to NPS 24 range, cross-checked across two independent reference tables. Convert to millimetres with 1 in = 25.4 mm.
| NPS | Flange OD O (in) | Bolt circle (in) | No. of bolts | Bolt hole (in) | Bolt size (in) |
|---|---|---|---|---|---|
| 1/2 | 3.50 | 2.38 | 4 | 5/8 | 1/2 |
| 3/4 | 3.88 | 2.75 | 4 | 5/8 | 1/2 |
| 1 | 4.25 | 3.12 | 4 | 5/8 | 1/2 |
| 1-1/4 | 4.62 | 3.50 | 4 | 5/8 | 1/2 |
| 1-1/2 | 5.00 | 3.88 | 4 | 5/8 | 1/2 |
| 2 | 6.00 | 4.75 | 4 | 3/4 | 5/8 |
| 2-1/2 | 7.00 | 5.50 | 4 | 3/4 | 5/8 |
| 3 | 7.50 | 6.00 | 4 | 3/4 | 5/8 |
| 4 | 9.00 | 7.50 | 8 | 3/4 | 5/8 |
| 5 | 10.00 | 8.50 | 8 | 7/8 | 3/4 |
| 6 | 11.00 | 9.50 | 8 | 7/8 | 3/4 |
| 8 | 13.50 | 11.75 | 8 | 7/8 | 3/4 |
| 10 | 16.00 | 14.25 | 12 | 1 | 7/8 |
| 12 | 19.00 | 17.00 | 12 | 1 | 7/8 |
| 14 | 21.00 | 18.75 | 12 | 1-1/8 | 1 |
| 16 | 23.50 | 21.25 | 16 | 1-1/8 | 1 |
| 18 | 25.00 | 22.75 | 16 | 1-1/4 | 1-1/8 |
| 20 | 27.50 | 25.00 | 20 | 1-1/4 | 1-1/8 |
| 24 | 32.00 | 29.50 | 20 | 1-3/8 | 1-1/4 |
Bolt holes are drilled on the bolt circle, straddling the centreline and equally spaced. The bolt hole is the bolt size plus 1/8 in clearance throughout (a 1/2 in bolt in a 5/8 in hole, a 3/4 in bolt in a 7/8 in hole, and so on). Class 150 keeps four bolts to NPS 3-1/2, steps to eight at NPS 4, and rises to twenty at NPS 20 to 24.
Two flanges bolt together only when the pressure class, NPS, bolt circle and bolt pattern all agree, so confirm all four before ordering. A Class 150 flange will not mate to a Class 300 flange of the same NPS even though the bore is the same — the outside diameter, bolt circle and hole count differ. A Class 150 ASME flange and a PN-rated EN 1092-1 flange of a similar size are likewise not interchangeable; the bolt circles and hole counts do not match. ASME B16.5 also defines the facing (the raised face is the common Class 150 facing) and the flange material group, which set the gasket and bolt grade for the temperature and pressure. The dimensions above are for the raised-face weld-neck flange; blind, slip-on, socket-weld, threaded and lap-joint Class 150 flanges to ASME B16.5 share the same outside diameter, bolt circle, bolt hole, bolt count and bolt size.
Dimensions are nominal ASME B16.5 values and provided for identification and cross-reference. Confirm against the controlling standard and the specific flange maker’s current data sheet before manufacture or procurement.