A 6-inch (NPS 6) ASME B16.5 flange has 8 bolt holes in Class 150 and 12 in Class 300. Both classes use 3/4 in bolts. The class stamped on the flange decides the drilling, so check it before you order bolts or draw the flange.
NPS 6 is the nominal pipe size for a 150 mm (DN150) pipe.
Class 150 and Class 300 at 6 inches
- Class 150, 6″ (150 mm): 8 bolts of 3/4 in diameter. The holes are 7/8 in (22.2 mm) diameter on a 9.50 in (241 mm) bolt circle, and the flange OD is 11.00 in (279 mm).
- Class 300, 6″: 12 bolts of 3/4 in diameter.
Hole position and spacing
- Hole position: The holes are equally spaced and straddle the centrelines, so no hole sits on the vertical or horizontal axis.
- Spacing: 45° apart for 8 holes (30° for 12 holes).
Australian flanges are different
AS 2129 and AS 4087 flanges use different drillings and are generally not interchangeable with ASME B16.5. Check which standard your flange follows, and match both flanges in a joint.
These are typical values only. Confirm the hole count, bolt circle and bolt size against the flange standard and your supplier’s current catalogue before ordering or drawing.
Working
Hole spacing for n equally spaced holes: \theta = (360^\circ)/(n) Class 150, n = 8: \theta = 45^\circ Class 300, n = 12: \theta = 30^\circ Hole diameter: (7)/(8) in = 22.2 mm Bolt diameter: (3)/(4) in = 19.1 mm Bolt circle: 9.50 in = 241 mm Flange OD: 11.00 in = 279 mm
References
- ASME B16.5 Pipe Flanges and Flanged Fittings (NPS 1/2 to NPS 24) – Bolting and drilling tables; check the relevant clause and edition
- AS 2129 Flanges for pipes, valves and fittings – Drilling and dimension tables; check the relevant clause
- AS 4087 Metallic flanges for waterworks purposes – Drilling and dimension tables; check the relevant clause
General information only. This is not engineering advice, design approval or certification. Have safety-critical designs checked by a qualified engineer (RPEQ in Queensland).
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