Flange Bolt Patterns & Dimensions (ANSI B16.5)
Standard dimensions for pipe flange bolt patterns according to ANSI/ASME B16.5. This defines the Bolt Circle Diameter (BCD), the number of holes, and the required bolt sizes for different pressure classes.
Class 150 Flanges
| Nominal Pipe Size (NPS) | Flange OD | Bolt Circle Dia. | Number of Holes | Required Bolt Size |
|---|---|---|---|---|
| 1" | 4.25" | 3.12" | 4 | 1/2" |
| 2" | 6.00" | 4.75" | 4 | 5/8" |
| 4" | 9.00" | 7.50" | 8 | 5/8" |
| 6" | 11.00" | 9.50" | 8 | 3/4" |
| 8" | 13.50" | 11.75" | 8 | 3/4" |
| 12" | 19.00" | 17.00" | 12 | 7/8" |
Class 300 Flanges (High Pressure)
| Nominal Pipe Size (NPS) | Flange OD | Bolt Circle Dia. | Number of Holes | Required Bolt Size |
|---|---|---|---|---|
| 1" | 4.88" | 3.50" | 4 | 5/8" |
| 2" | 6.50" | 5.00" | 8 | 5/8" |
| 4" | 10.00" | 7.88" | 8 | 3/4" |
| 6" | 12.50" | 10.62" | 12 | 3/4" |
| 8" | 15.00" | 13.00" | 12 | 7/8" |
| 12" | 20.50" | 17.75" | 16 | 1 1/8" |