Threaded Flange Dimensions
Tapped with an ASME B1.20.1 NPT taper thread and screwed onto matching pipe, with no welding at all. That makes it the flange for places where a hot work permit is impossible.
- Standard
- ASME B16.5
- Abbreviation
- THD
- Pressure classes
- 7
- Size range
- NPS 1/2 – NPS 24
- Typical service
- Low-pressure utility piping and hazardous areas where welding is banned.
Dimensions by pressure class
Strengths
- No welding, so usable in flammable or explosive areas
- Fast field installation with hand tools
Limitations
- Not for cyclic, high-temperature or vibrating service — the thread loosens
- Thread root reduces the effective wall; needs thick-wall pipe
Class 150 dimensions
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| Size | Flange OD | Thickness | Bolt circle | Bolts | Bolt dia. | Raised face OD |
|---|---|---|---|---|---|---|
| NPS 1/2 | 3.5088.90 mm | 0.4411.18 mm | 2.3860.45 mm | 4 | 1/2 in | 1.3835.05 mm |
| NPS 3/4 | 3.8898.55 mm | 0.5012.70 mm | 2.7569.85 mm | 4 | 1/2 in | 1.6942.93 mm |
| NPS 1 | 4.25107.95 mm | 0.5614.22 mm | 3.1279.25 mm | 4 | 1/2 in | 2.0050.80 mm |
| NPS 1 1/4 | 4.62117.35 mm | 0.6215.75 mm | 3.5088.90 mm | 4 | 1/2 in | 2.5063.50 mm |
| NPS 1 1/2 | 5.00127.00 mm | 0.6917.53 mm | 3.8898.55 mm | 4 | 1/2 in | 2.8873.15 mm |
| NPS 2 | 6.00152.40 mm | 0.7519.05 mm | 4.75120.65 mm | 4 | 5/8 in | 3.6291.95 mm |
| NPS 2 1/2 | 7.00177.80 mm | 0.8822.35 mm | 5.50139.70 mm | 4 | 5/8 in | 4.12104.65 mm |
| NPS 3 | 7.50190.50 mm | 0.9423.88 mm | 6.00152.40 mm | 4 | 5/8 in | 5.00127.00 mm |
| NPS 3 1/2 | 8.50215.90 mm | 0.9423.88 mm | 7.00177.80 mm | 8 | 5/8 in | 5.50139.70 mm |
| NPS 4 | 9.00228.60 mm | 0.9423.88 mm | 7.50190.50 mm | 8 | 5/8 in | 6.19157.23 mm |
| NPS 5 | 10.00254.00 mm | 0.9423.88 mm | 8.50215.90 mm | 8 | 3/4 in | 7.31185.67 mm |
| NPS 6 | 11.00279.40 mm | 1.0025.40 mm | 9.50241.30 mm | 8 | 3/4 in | 8.50215.90 mm |
| NPS 8 | 13.50342.90 mm | 1.1228.45 mm | 11.75298.45 mm | 8 | 3/4 in | 10.62269.75 mm |
| NPS 10 | 16.00406.40 mm | 1.1930.23 mm | 14.25361.95 mm | 12 | 7/8 in | 12.75323.85 mm |
| NPS 12 | 19.00482.60 mm | 1.2531.75 mm | 17.00431.80 mm | 12 | 7/8 in | 15.00381.00 mm |
| NPS 14 | 21.00533.40 mm | 1.3835.05 mm | 18.75476.25 mm | 12 | 1 in | 16.25412.75 mm |
| NPS 16 | 23.50596.90 mm | 1.4436.58 mm | 21.25539.75 mm | 16 | 1 in | 18.50469.90 mm |
| NPS 18 | 25.00635.00 mm | 1.5639.62 mm | 22.75577.85 mm | 16 | 1 1/8 in | 21.00533.40 mm |
| NPS 20 | 27.50698.50 mm | 1.6942.93 mm | 25.00635.00 mm | 20 | 1 1/8 in | 23.00584.20 mm |
| NPS 24 | 32.00812.80 mm | 1.8847.75 mm | 29.50749.30 mm | 20 | 1 1/4 in | 27.25692.15 mm |
Higher classes are on the Class 300 page and above.
Common questions
When should I use a threaded flange?
Low-pressure utility piping and hazardous areas where welding is banned.
What pressure classes does a threaded flange come in?
ASME B16.5 publishes the threaded flange in Class 150, Class 300, Class 400, Class 600, Class 900, Class 1500 and Class 2500, in sizes NPS 1/2 through NPS 24. Above NPS 24 large-diameter flanges are covered by ASME B16.47 instead.
Does the flange face type change these dimensions?
The flange outside diameter, bolt circle and bolting are the same whatever the face. What changes is the facing itself and the flange thickness measurement: B16.5 thickness excludes the raised face, so a Class 300 raised-face flange is 0.06 in thicker overall than the tabulated figure. Ring-type joint flanges are grooved instead and are dimensioned separately.