Class 400 Welding Neck Flange dimensions follow the ASME B16.5 standard, and like other pressure classes, the dimensions will vary depending on the nominal pipe size (NPS) of the flange. Here are the general dimensions for a Class 400 Welding Neck Flange for common sizes:
| Flange NPS | Inside | Outside | Bolt Circle | Raised Face | Raised Face | H | H1 | Raised Face | T1 | Flat Face | Bolt Hole | No. of |
| Diameter | Diameter | (BC) | (R) | (RF) | Thickness (T) | Thickness (T2) | (B) | Bolt Holes | ||||
| 1/2″ | .55″ | 3.75″ | 2.62″ | 1.38″ | .250″ | 1.50″ | 0.84″ | 2.31″ | 0.56″ | 2.06″ | 0.62″ | 4 |
| 3/4″ | .74″ | 4.62″ | 3.25″ | 1.69″ | .250″ | 1.88″ | 1.05″ | 2.50″ | 0.62″ | 2.25″ | 0.75″ | 4 |
| 1″ | .96″ | 4.88″ | 3.50″ | 2.00″ | .250″ | 2.12″ | 1.32″ | 2.69″ | 0.69″ | 2.44″ | 0.75″ | 4 |
| 1-1/4″ | 1.28″ | 5.25″ | 3.88″ | 2.50″ | .250″ | 2.50″ | 1.66″ | 2.87″ | 0.81″ | 2.62″ | 0.75″ | 4 |
| 1-1/2″ | 1.50″ | 6.12″ | 4.50″ | 2.88″ | .250″ | 2.75″ | 1.90″ | 3.00″ | 0.88″ | 2.75″ | 0.88″ | 4 |
| 2″ | 1.94″ | 6.50″ | 5.00″ | 3.62″ | .250″ | 3.31″ | 2.38″ | 3.13″ | 1.00″ | 2.88″ | 0.75″ | 8 |
| 2-1/2″ | 2.32″ | 7.50″ | 5.88″ | 4.12″ | .250″ | 3.94″ | 2.88″ | 3.37″ | 1.12″ | 3.12″ | 0.88″ | 8 |
| 3″ | 2.90″ | 8.25″ | 6.62″ | 5.00″ | .250″ | 4.62″ | 3.50″ | 3.50″ | 1.25″ | 3.25″ | 0.88″ | 8 |
| 3-1/2″ | 3.36″ | 9.00″ | 7.25″ | 5.50″ | .250″ | 5.25″ | 4.00″ | 3.63″ | 1.38″ | 3.38″ | 1.00″ | 8 |
| 4″ | 3.83″ | 10.00″ | 7.88″ | 6.19″ | .250″ | 5.75″ | 4.50″ | 3.75″ | 1.38″ | 3.50″ | 1.00″ | 8 |
| 5″ | 4.81″ | 11.00″ | 9.25″ | 7.31″ | .250″ | 7.00″ | 5.56″ | 4.25″ | 1.50″ | 4.00″ | 1.00″ | 8 |
| 6″ | 5.76″ | 12.50″ | 10.62″ | 8.50″ | .250″ | 8.12″ | 6.63″ | 4.31″ | 1.62″ | 4.06″ | 1.00″ | 12 |
| 8″ | 7.63″ | 15.00″ | 13.00″ | 10.62″ | .250″ | 10.25″ | 8.63″ | 4.87″ | 1.88″ | 4.62″ | 1.12″ | 12 |
| 10″ | 9.75″ | 17.50″ | 15.25″ | 12.75″ | .250″ | 12.62″ | 10.75″ | 5.13″ | 2.12″ | 4.88″ | 1.25″ | 16 |
| 12″ | 11.75″ | 20.50″ | 17.75″ | 15.00″ | .250″ | 14.75″ | 12.75″ | 5.63″ | 2.25″ | 5.38″ | 1.38″ | 16 |
| 14″ | 13.00″ | 23.00″ | 20.25″ | 16.25″ | .250″ | 16.75″ | 14.00″ | 6.13″ | 2.38″ | 5.88″ | 1.38″ | 20 |
| 16″ | 15.00″ | 25.50″ | 22.50″ | 18.50″ | .250″ | 19.00″ | 16.00″ | 6.25″ | 2.50″ | 6.00″ | 1.50″ | 20 |
| 18″ | 17.00″ | 28.00″ | 24.75″ | 21.00″ | .250″ | 21.00″ | 18.00″ | 6.75″ | 2.62″ | 6.50″ | 1.50″ | 24 |
| 20″ | 19.00″ | 30.50″ | 27.00″ | 23.00″ | .250″ | 23.12″ | 20.00″ | 6.87″ | 2.75″ | 6.62″ | 1.62″ | 24 |
| 22″ | 21.00″ | 33.00″ | 29.25″ | 25.25″ | .250″ | 25.25″ | 22.00″ | 7.00″ | 2.88″ | 6.75″ | 1.75″ | 24 |
| 24″ | 23.00″ | 36.00″ | 32.00″ | 27.25″ | .250″ | 27.62″ | 24.00″ | 7.13″ | 3.00″ | 6.88″ | 1.88″ | 24 |
Nominal Pipe Size (NPS): Ranges from 1/2 inch (DN 15) to 24 inches (DN 600) and larger.
Outside Diameter (OD): Varies with NPS. For example, the OD of a 1/2-inch flange is approximately 4.25 inches, while the OD of a 24-inch flange is around 32.63 inches.
Bolt Circle Diameter (BCD): Increases with the size of the flange. For instance, the BCD of a 1/2-inch flange is approximately 3.38 inches, while the BCD of a 24-inch flange is around 29.5 inches.
Number of Bolt Holes: Varies with NPS. Smaller sizes may have fewer bolt holes (e.g., 4), while larger sizes may have more (e.g., 20).
Bolt Hole Diameter: The diameter of the bolt holes varies with NPS. For example, the bolt hole diameter for a 1/2-inch flange is approximately 0.88 inches.
Hub Diameter: The diameter of the raised face at the base of the flange increases with the size of the flange.
Overall Length Through Hub (LTH): This dimension, which is the distance from the face of the flange to the end of the hub, also increases with the size of the flange.
Flange Thickness: The thickness of the flange varies based on the pressure class.
Please note that these dimensions are general and specific dimensions may vary depending on the manufacturer and the standards being followed. For accurate and detailed dimensions, it's recommended to refer to the ASME B16.5 standard or consult the manufacturer's specifications for the specific flange size and class.
