Class 300 Blind Flange Dimensions
ASME B16.5 dimensions and bolting for the Class 300 blind flange, NPS 1/2 through NPS 24.
- Standard
- ASME B16.5
- Flange type
- Blind Flange
- Pressure class
- Class 300
- Size range
- NPS 1/2 – NPS 24
- Raised face height
- 0.06 in (1.5 mm)
- Rating at 100 °F (A105)
- 740 psig (51.0 bar)
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 | 3.7595.25 mm | 0.5614.22 mm | 2.6266.55 mm | 4 | 1/2 in | 1.3835.05 mm |
| NPS 3/4 | 4.62117.35 mm | 0.6215.75 mm | 3.2582.55 mm | 4 | 5/8 in | 1.6942.93 mm |
| NPS 1 | 4.88123.95 mm | 0.6917.53 mm | 3.5088.90 mm | 4 | 5/8 in | 2.0050.80 mm |
| NPS 1 1/4 | 5.25133.35 mm | 0.7519.05 mm | 3.8898.55 mm | 4 | 5/8 in | 2.5063.50 mm |
| NPS 1 1/2 | 6.12155.45 mm | 0.8120.57 mm | 4.50114.30 mm | 4 | 3/4 in | 2.8873.15 mm |
| NPS 2 | 6.50165.10 mm | 0.8822.35 mm | 5.00127.00 mm | 8 | 5/8 in | 3.6291.95 mm |
| NPS 2 1/2 | 7.50190.50 mm | 1.0025.40 mm | 5.88149.35 mm | 8 | 3/4 in | 4.12104.65 mm |
| NPS 3 | 8.25209.55 mm | 1.1228.45 mm | 6.62168.15 mm | 8 | 3/4 in | 5.00127.00 mm |
| NPS 3 1/2 | 9.00228.60 mm | 1.1930.23 mm | 7.25184.15 mm | 8 | 3/4 in | 5.50139.70 mm |
| NPS 4 | 10.00254.00 mm | 1.2531.75 mm | 7.88200.15 mm | 8 | 3/4 in | 6.19157.23 mm |
| NPS 5 | 11.00279.40 mm | 1.3835.05 mm | 9.25234.95 mm | 8 | 3/4 in | 7.31185.67 mm |
| NPS 6 | 12.50317.50 mm | 1.4436.58 mm | 10.62269.75 mm | 12 | 3/4 in | 8.50215.90 mm |
| NPS 8 | 15.00381.00 mm | 1.6241.15 mm | 13.00330.20 mm | 12 | 7/8 in | 10.62269.75 mm |
| NPS 10 | 17.50444.50 mm | 1.8847.75 mm | 15.25387.35 mm | 16 | 1 in | 12.75323.85 mm |
| NPS 12 | 20.50520.70 mm | 2.0050.80 mm | 17.75450.85 mm | 16 | 1 1/8 in | 15.00381.00 mm |
| NPS 14 | 23.00584.20 mm | 2.1253.85 mm | 20.25514.35 mm | 20 | 1 1/8 in | 16.25412.75 mm |
| NPS 16 | 25.50647.70 mm | 2.2557.15 mm | 22.50571.50 mm | 20 | 1 1/4 in | 18.50469.90 mm |
| NPS 18 | 28.00711.20 mm | 2.3860.45 mm | 24.75628.65 mm | 24 | 1 1/4 in | 21.00533.40 mm |
| NPS 20 | 30.50774.70 mm | 2.5063.50 mm | 27.00685.80 mm | 24 | 1 1/4 in | 23.00584.20 mm |
| NPS 24 | 36.00914.40 mm | 2.7569.85 mm | 32.00812.80 mm | 24 | 1 1/2 in | 27.25692.15 mm |
Flange thickness excludes the raised face. Bolt diameter is nominal; stud bolts are normally ASTM A193 B7 with A194 2H nuts.
A blind flange has no bore and no hub, so the flange outside diameter, thickness, bolt circle and bolting are the whole of its dimensional definition. Thickness shown is the minimum required by B16.5 — many mills supply heavier.
Each size above links to its own page, with an approximate weight and the end thrust at the rated pressure.
Common questions
How many bolts does a Class 300 blind flange use?
NPS 1/2 takes 4 × 1/2 in; NPS 3/4 takes 4 × 5/8 in; NPS 1 takes 4 × 5/8 in; NPS 1 1/4 takes 4 × 5/8 in; NPS 1 1/2 takes 4 × 3/4 in. Bolt count rises with size — see the table above for the full range.
What pressure is a Class 300 flange rated for?
Class is a designation, not a pressure. A Class 300 flange in A105 carbon steel is rated 740 psig (51.0 bar) at 100 °F, and that rating falls as metal temperature rises. In stainless the same class starts lower at ambient but holds up far better in the heat — see the P-T rating tables.
Will a Class 300 flange bolt to a Class 150 flange?
No. Bolt circle diameter, bolt count and bolt size all change with class, so flanges of different classes in the same NPS will not mate. The only exceptions inside B16.5 are the deliberate ones the standard calls out, such as Class 400 sharing Class 600 dimensions in NPS 1/2 through 3 1/2.