# ASME B16.5 flange bolt patterns: bolt circle, number of holes and bolt size, Class 150 and 300, NPS ½ to 24

> What is the bolt pattern of an ASME B16.5 flange (bolt circle, number of holes, bolt size) by NPS and class?

- Category: Tri-clamp & pipe › Pipe, tube & threads
- Kind: Standard part
- Basis: ASME B16.5 bolt circle and hole counts from Texas Flange (inch) checked against Project Materials (mm); bolt diameter and stud length from Wermac's stud tables
- Page: https://xemstudio.com/objects/asme-b16-5-flange-bolt-patterns/ · JSON: https://xemstudio.com/api/geometry?object=asme-b16-5-flange-bolt-patterns · Plain text: https://xemstudio.com/objects/asme-b16-5-flange-bolt-patterns/sheet.txt
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**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- Bolt circle, hole count and bolt size are the same for weld-neck, slip-on, blind, lap-joint, socket-weld and threaded flanges of one NPS and class.
- Hole diameter is the bolt diameter plus 1/8 in. Stud length is for a raised-face joint (two flanges with 1/16 in raised faces, a gasket, two nuts) as printed in Wermac's tables; ring-joint studs are longer and are not listed.
- Bolt holes straddle the centrelines; there is no hole on the vertical axis (the usual B16.5 layout, not stated in the tables cited).
- Bolt circle is printed in inch; mm is the inch value × 25.4. Class 150 and Class 300 flange files with these holes are on the class pages (blind and slip-on flanges at every NPS).
- Class 600 and above, and NPS 22, are not listed: no clean multi-source table was available.

## Sizes

| class | NPS | holes | bolt dia, in | hole dia, in | bolt circle, in (mm) | stud length RF, in |
|---|---|---|---|---|---|---|
| 150 | 1/2 | 4 | 0.5 | 0.625 | 2.375 (60.3) | 2.25 |
| 150 | 3/4 | 4 | 0.5 | 0.625 | 2.750 (69.8) | 2.5 |
| 150 | 1 | 4 | 0.5 | 0.625 | 3.125 (79.4) | 2.5 |
| 150 | 1-1/4 | 4 | 0.5 | 0.625 | 3.500 (88.9) | 2.75 |
| 150 | 1-1/2 | 4 | 0.5 | 0.625 | 3.875 (98.4) | 2.75 |
| 150 | 2 | 4 | 0.625 | 0.75 | 4.750 (120.6) | 3.25 |
| 150 | 2-1/2 | 4 | 0.625 | 0.75 | 5.500 (139.7) | 3.5 |
| 150 | 3 | 4 | 0.625 | 0.75 | 6.000 (152.4) | 3.5 |
| 150 | 3-1/2 | 8 | 0.625 | 0.75 | 7.000 (177.8) | 3.5 |
| 150 | 4 | 8 | 0.625 | 0.75 | 7.500 (190.5) | 3.5 |
| 150 | 5 | 8 | 0.75 | 0.875 | 8.500 (215.9) | 3.75 |
| 150 | 6 | 8 | 0.75 | 0.875 | 9.500 (241.3) | 4 |
| 150 | 8 | 8 | 0.75 | 0.875 | 11.750 (298.4) | 4.25 |
| 150 | 10 | 12 | 0.875 | 1 | 14.250 (361.9) | 4.5 |
| 150 | 12 | 12 | 0.875 | 1 | 17.000 (431.8) | 4.75 |
| 150 | 14 | 12 | 1 | 1.125 | 18.750 (476.2) | 5.25 |
| 150 | 16 | 16 | 1 | 1.125 | 21.250 (539.8) | 5.25 |
| 150 | 18 | 16 | 1.125 | 1.25 | 22.750 (577.9) | 5.75 |
| 150 | 20 | 20 | 1.125 | 1.25 | 25.000 (635.0) | 6.25 |
| 150 | 24 | 20 | 1.25 | 1.375 | 29.500 (749.3) | 6.75 |
| 300 | 1/2 | 4 | 0.5 | 0.625 | 2.625 (66.7) | 2.5 |
| 300 | 3/4 | 4 | 0.625 | 0.75 | 3.250 (82.5) | 3 |
| 300 | 1 | 4 | 0.625 | 0.75 | 3.500 (88.9) | 3 |
| 300 | 1-1/4 | 4 | 0.625 | 0.75 | 3.875 (98.4) | 3.25 |
| 300 | 1-1/2 | 4 | 0.75 | 0.875 | 4.500 (114.3) | 3.5 |
| 300 | 2 | 8 | 0.625 | 0.75 | 5.000 (127.0) | 3.5 |
| 300 | 2-1/2 | 8 | 0.75 | 0.875 | 5.875 (149.2) | 4 |
| 300 | 3 | 8 | 0.75 | 0.875 | 6.625 (168.3) | 4.25 |
| 300 | 3-1/2 | 8 | 0.75 | 0.875 | 7.250 (184.1) | 4.25 |
| 300 | 4 | 8 | 0.75 | 0.875 | 7.875 (200.0) | 4.5 |
| 300 | 5 | 8 | 0.75 | 0.875 | 9.250 (234.9) | 4.75 |
| 300 | 6 | 12 | 0.75 | 0.875 | 10.625 (269.9) | 4.75 |
| 300 | 8 | 12 | 0.875 | 1 | 13.000 (330.2) | 5.5 |
| 300 | 10 | 16 | 1 | 1.125 | 15.250 (387.3) | 6.25 |
| 300 | 12 | 16 | 1.125 | 1.25 | 17.750 (450.8) | 6.75 |
| 300 | 14 | 20 | 1.125 | 1.25 | 20.250 (514.4) | 7 |
| 300 | 16 | 20 | 1.25 | 1.375 | 22.500 (571.5) | 7.5 |
| 300 | 18 | 24 | 1.25 | 1.375 | 24.750 (628.6) | 7.75 |
| 300 | 20 | 24 | 1.25 | 1.375 | 27.000 (685.8) | 8 |
| 300 | 24 | 24 | 1.5 | 1.625 | 32.000 (812.8) | 9 |

## Where the files are

- Texas Flange: [ANSI B16.5 Class 150 forged flange dimensions (inch)](https://texasflange.com/products/flange-dims-weights/ansi-b16-5-forged-flanges/class-150/) — web — Publisher's page; dimensions are facts
- Texas Flange: [ANSI B16.5 Class 300 forged flange dimensions (inch)](https://www.texasflange.com/products/flange-dims-weights/ansi-b16-5-forged-flanges/class-300/) — web — Publisher's page; dimensions are facts
- Wermac: [Weld neck flanges ASME B16.5 Class 150 (inch) with stud bolt table](https://wermac.org/flanges/dimensions_weldneck_in_asme-b16-5.html) — web — Publisher's page; dimensions are facts
- Wermac: [Stud bolts for ASME B16.5 Class 300 flanges (inch)](https://www.wermac.org/bolts/dimensions_stud-bolts_class-300_inches.html) — web — Publisher's page; dimensions are facts
- Project Materials: [Slip-on flange dimensions ASME B16.5 Class 150 and 300 (mm)](https://blog.projectmaterials.com/flanges/slip-on-flange-dimensions-asme-ansi/) — web — Publisher's page; dimensions are facts

## Questions

**What is the bolt pattern of a 2 inch 150# flange?**

4 holes of 0.75 in on a 4.750 in (120.6 mm) bolt circle, for 0.625 in bolts.

**What is the bolt pattern of a 6 inch 300# flange?**

12 holes of 0.875 in on a 10.625 in (269.9 mm) bolt circle, for 0.75 in bolts.

**How many bolts does a 4 inch 150# flange have?**

8 bolts of 5/8 in on a 7.5 in bolt circle.

**How do the 150# and 300# bolt patterns differ?**

300# flanges use a larger bolt circle, usually larger bolts and, from NPS 2 up, more holes at the same size.

## Fits with

- [ASME B16.5 Class 150 pipe flanges, NPS ½ to 24: dimensions, bolt circle, slip-on and blind](https://xemstudio.com/objects/asme-b16-5-class-150-flanges/)
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