ASME/ANSI B16.5-1996 Pipe Flanges and Flanged Fittings - Class 400 Flanges - outside and inside diameters, bolt circles, numbers and diameters of bolts for Weld neck, Threaded, Slip-on, Lap joint, Socket weld and Blind flanges. Carbon and stainless steel qualities according ASME B16.5 Table 1A.
| Pipe Size (inches) |
Outside Diameter (inches) |
Inside Diameter (inches) |
Number of Bolt Holes | Bolt Hole Diameter (inches) 1) |
Bolt Circle (inches) |
| 1/2 | 3-3/4 | 0.88 | 4 | 5/8 | 2-5/8 |
| 3/4 | 4-5/8 | 1.09 | 4 | 3/4 | 3-1/4 |
| 1 | 4-7/8 | 1.36 | 4 | 3/4 | 3-1/2 |
| 1-1/4 | 5-1/4 | 1.70 | 4 | 3/4 | 3-7/8 |
| 1-1/2 | 6-1/8 | 1.95 | 4 | 7/8 | 4-1/2 |
| 2 | 6-1/2 | 2.44 | 8 | 3/4 | 5 |
| 2-1/2 | 7-1/2 | 2.94 | 8 | 7/8 | 5-7/8 |
| 3 | 8-1/4 | 3.57 | 8 | 7/8 | 6-5/8 |
| 3-1/2 | 9 | 4.07 | 8 | 1 | 7-1/4 |
| 4 | 10 | 4.57 | 8 | 1 | 8-7/8 |
| 5 | 11 | 5.66 | 8 | 1 | 9-1/4 |
| 6 | 12-1/2 | 6.72 | 12 | 1 | 10-5/8 |
| 8 | 15 | 8.72 | 12 | 1-1/8 | 13 |
| 10 | 17-1/2 | 10.88 | 16 | 1-1/4 | 15-1/4 |
| 12 | 20-1/2 | 12.88 | 16 | 1-3/8 | 17-3/4 |
| 14 | 23 | 14.14 | 20 | 1-3/8 | 20-1/4 |
| 16 | 25-1/2 | 16.16 | 20 | 1-1/2 | 22-1/2 |
| 18 | 28 | 18.18 | 24 | 1-1/2 | 24-3/4 |
| 20 | 30-1/2 | 20.20 | 24 | 1-5/8 | 27 |
| 24 | 36 | 24.25 | 24 | 1-7/8 | 32 |
1) Recommended bolts are 1/8 smaller than the nominal bolt hole diameters shown.