The dimensions of a Class 300 Welding Neck Flange, according to ASME B16.5 standards, will vary depending on the size of the flange. Below are the general dimensions for a Class 300 Welding Neck Flange for some 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″ | 0.62″ | 3.50″ | 2.38″ | 1.38″ | .063″ | 1.19″ | 0.84″ | 1.88″ | .38″ | 1.82″ | .62″ | 4 |
| 3/4″ | 0.82″ | 3.88″ | 2.75″ | 1.69″ | .063″ | 1.50″ | 1.05″ | 2.06″ | .44″ | 2.00″ | .62″ | 4 |
| 1″ | 1.05″ | 4.25″ | 3.12″ | 2.00″ | .063″ | 1.94″ | 1.32″ | 2.19″ | .50″ | 2.13″ | .62″ | 4 |
| 1-1/4″ | 1.38″ | 4.62″ | 3.50″ | 2.50″ | .063″ | 2.31″ | 1.66″ | 2.25″ | .56″ | 2.19″ | .62″ | 4 |
| 1-1/2″ | 1.61″ | 5.00″ | 3.88″ | 2.88″ | .063″ | 2.56″ | 1.90″ | 2.44″ | .62″ | 2.38″ | .62″ | 4 |
| 2″ | 2.07″ | 6.00″ | 4.75″ | 3.62″ | .063″ | 3.06″ | 2.38″ | 2.50″ | .69″ | 2.44″ | .75″ | 4 |
| 2-1/2″ | 2.47″ | 7.00″ | 5.50″ | 4.12″ | .063″ | 3.56″ | 2.88″ | 2.75″ | .82″ | 2.69″ | .75″ | 4 |
| 3″ | 3.07″ | 7.50″ | 6.00″ | 5.00″ | .063″ | 4.25″ | 3.50″ | 2.75″ | .88″ | 2.69″ | .75″ | 4 |
| 3-1/2″ | 3.55″ | 8.50″ | 7.00″ | 5.50″ | .063″ | 4.81″ | 4.00″ | 2.81″ | .88″ | 2.75″ | .75″ | 8 |
| 4″ | 4.03″ | 9.00″ | 7.50″ | 6.19″ | .063″ | 5.31″ | 4.50″ | 3.00″ | .88″ | 2.94″ | .75″ | 8 |
| 5″ | 5.05″ | 10.00″ | 8.50″ | 7.31″ | .063″ | 6.44″ | 5.56″ | 3.50″ | .88″ | 3.44″ | .88″ | 8 |
| 6″ | 6.07″ | 11.00″ | 9.50″ | 8.50″ | .063″ | 7.56″ | 6.63″ | 3.50″ | .94″ | 3.44″ | .88″ | 8 |
| 8″ | 7.98″ | 13.50″ | 11.75″ | 10.62″ | .063″ | 9.69″ | 8.63″ | 4.00″ | 1.06″ | 3.94″ | .88″ | 8 |
| 10″ | 10.02″ | 16.00″ | 14.25″ | 12.75″ | .063″ | 12.00″ | 10.75″ | 4.00″ | 1.13″ | 3.94″ | 1.00″ | 12 |
| 12″ | 12.00″ | 19.00″ | 17.00″ | 15.00″ | .063″ | 14.38″ | 12.75″ | 4.50″ | 1.19″ | 4.44″ | 1.00″ | 12 |
| 14″ | 13.25″ | 21.00″ | 18.75″ | 16.25″ | .063″ | 15.75″ | 14.00″ | 5.00″ | 1.32″ | 4.94″ | 1.12″ | 12 |
| 16″ | 15.25″ | 23.50″ | 21.25″ | 18.50″ | .063″ | 18.00″ | 16.00″ | 5.00″ | 1.38″ | 4.94″ | 1.12″ | 16 |
| 18″ | 17.25″ | 25.00″ | 22.75″ | 21.00″ | .063″ | 19.88″ | 18.00″ | 5.50″ | 1.50″ | 5.44″ | 1.25″ | 16 |
| 20″ | 19.25″ | 27.50″ | 25.00″ | 23.00″ | .063″ | 22.00″ | 20.00″ | 5.69″ | 1.63″ | 5.63″ | 1.25″ | 20 |
| 22″ | 21.25″ | 29.50″ | 27.25″ | 25.25″ | .063″ | 24.25″ | 22.00″ | 5.88″ | 1.75″ | 5.82″ | 1.38″ | 20 |
| 24″ | 23.25″ | 32.00″ | 29.50″ | 27.25″ | .063″ | 26.12″ | 24.00″ | 6.00″ | 1.82″ | 5.94″ | 1.38″ | 20 |
Nominal Pipe Size (NPS): 1/2 inch (DN 15) to 24 inches (DN 600) and larger.
Outside Diameter (OD): The OD varies with NPS. For instance, the OD of a 1/2-inch flange is approximately 3.88 inches, while the OD of a 24-inch flange is around 32.38 inches.
Bolt Circle Diameter (BCD): This dimension increases with the size of the flange. For example, the BCD of a 1/2-inch flange is approximately 3.25 inches, while the BCD of a 24-inch flange is around 29.5 inches.
Number of Bolt Holes: The 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 remember that these are general dimensions, and specific dimensions might differ based on the manufacturer and the standards being followed. For precise and detailed dimensions, it's advisable to refer to the ASME B16.5 standard or consult the manufacturer's specifications for the particular flange size and class.
