Flange Bolt-Pattern & Dimension Chart (ASME B16.5 Class 150)
This chart gives the bolt circle diameter, number of bolts, and bolt size for ASME B16.5 Class 150 flanges. Because Class 150 and iron ASME B16.1 Class 125 share the same drilling, the same pattern applies to most ductile-iron valves and companion flanges.
Class 150 / Class 125 bolt pattern
Verify against the current ASME standard for critical or high-pressure work.
| Nominal pipe size | Bolt circle (in) | No. of bolts | Bolt diameter (in) |
|---|---|---|---|
| 1/2" | 2.38 | 4 | 1/2 |
| 3/4" | 2.75 | 4 | 1/2 |
| 1" | 3.12 | 4 | 1/2 |
| 1-1/4" | 3.50 | 4 | 1/2 |
| 1-1/2" | 3.88 | 4 | 1/2 |
| 2" | 4.75 | 4 | 5/8 |
| 2-1/2" | 5.50 | 4 | 5/8 |
| 3" | 6.00 | 4 | 5/8 |
| 4" | 7.50 | 8 | 5/8 |
| 5" | 8.50 | 8 | 3/4 |
| 6" | 9.50 | 8 | 3/4 |
| 8" | 11.75 | 8 | 3/4 |
| 10" | 14.25 | 12 | 7/8 |
| 12" | 17.00 | 12 | 7/8 |
How to use it
Match the bolt circle and bolt count to confirm two flanges mate. Remember Class 150 and Class 300 are not interchangeable — Class 300 uses a different (larger) pattern. Always tighten flange bolts in a star/criss-cross sequence in stages for even gasket compression.
Related
See the flange selection guide for types and pressure classes, and browse flanges.