2-1/2 inch Class 150 flange dimensions
ASME B16.5 Class 150 flange dimensions for 2-1/2 inch (DN 65) pipe. The same bolting dimensions apply to weld neck, slip-on, blind, socket weld, threaded and lap joint flanges of this size and class.
| Nominal size | 2-1/2" (DN 65) |
| Pipe OD (bore end) | 73.0 mm |
| Flange outside diameter | 180 mm (7.09 in) |
| Minimum thickness (incl. 1.6 mm RF) | 20.7 mm (0.81 in) |
| Bolt circle diameter (PCD) | 139.7 mm (5.50 in) |
| Number of bolt holes | 4 |
| Bolt hole diameter | 0.75 in (19.0 mm) |
| Stud bolt diameter | 5/8" UNC |
| Raised face height | 1.6 mm (1/16 in) |
A complete 2-1/2" Class 150 joint needs 4 stud bolts of 5/8" diameter with 8 heavy hex nuts and one gasket.
Class 150 vs Class 300 — 2-1/2"
| Dimension | Class 150 | Class 300 |
|---|---|---|
| OD | 180 mm | 190 mm |
| Thickness | 20.7 mm | 23.9 mm |
| Bolt circle | 139.7 mm | 149.2 mm |
| Bolts | 4 × 5/8" | 8 × 3/4" |
Class 150 and Class 300 flanges do not bolt together — see 2-1/2" Class 300.
Frequently asked questions
What is the OD of a 2-1/2 inch Class 150 flange?
180 mm (7.09 in) per ASME B16.5.
How many bolts does a 2-1/2 inch Class 150 flange have?
4 bolts of 5/8 inch diameter in 0.75 inch holes on a 139.7 mm bolt circle.
What is the thickness of a 2-1/2 inch Class 150 flange?
The minimum flange thickness is 20.7 mm, including the 1.6 mm raised face.
Last updated 2026-11-02