20 inch Class 150 flange dimensions
ASME B16.5 Class 150 flange dimensions for 20 inch (DN 500) 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 | 20" (DN 500) |
| Pipe OD (bore end) | 508.0 mm |
| Flange outside diameter | 700 mm (27.56 in) |
| Minimum thickness (incl. 1.6 mm RF) | 41.3 mm (1.63 in) |
| Bolt circle diameter (PCD) | 635.0 mm (25.00 in) |
| Number of bolt holes | 20 |
| Bolt hole diameter | 1.25 in (31.8 mm) |
| Stud bolt diameter | 1-1/8" UNC |
| Raised face height | 1.6 mm (1/16 in) |
A complete 20" Class 150 joint needs 20 stud bolts of 1-1/8" diameter with 40 heavy hex nuts and one gasket.
Class 150 vs Class 300 — 20"
| Dimension | Class 150 | Class 300 |
|---|---|---|
| OD | 700 mm | 775 mm |
| Thickness | 41.3 mm | 62.0 mm |
| Bolt circle | 635.0 mm | 685.8 mm |
| Bolts | 20 × 1-1/8" | 24 × 1-1/4" |
Class 150 and Class 300 flanges do not bolt together — see 20" Class 300.
Frequently asked questions
What is the OD of a 20 inch Class 150 flange?
700 mm (27.56 in) per ASME B16.5.
How many bolts does a 20 inch Class 150 flange have?
20 bolts of 1-1/8 inch diameter in 1.25 inch holes on a 635.0 mm bolt circle.
What is the thickness of a 20 inch Class 150 flange?
The minimum flange thickness is 41.3 mm, including the 1.6 mm raised face.
Last updated 2026-11-02