18 inch Class 150 flange dimensions
ASME B16.5 Class 150 flange dimensions for 18 inch (DN 450) 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 | 18" (DN 450) |
| Pipe OD (bore end) | 457.0 mm |
| Flange outside diameter | 635 mm (25.00 in) |
| Minimum thickness (incl. 1.6 mm RF) | 38.1 mm (1.50 in) |
| Bolt circle diameter (PCD) | 577.9 mm (22.75 in) |
| Number of bolt holes | 16 |
| 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 18" Class 150 joint needs 16 stud bolts of 1-1/8" diameter with 32 heavy hex nuts and one gasket.
Class 150 vs Class 300 — 18"
| Dimension | Class 150 | Class 300 |
|---|---|---|
| OD | 635 mm | 710 mm |
| Thickness | 38.1 mm | 58.8 mm |
| Bolt circle | 577.9 mm | 628.6 mm |
| Bolts | 16 × 1-1/8" | 24 × 1-1/4" |
Class 150 and Class 300 flanges do not bolt together — see 18" Class 300.
Frequently asked questions
What is the OD of a 18 inch Class 150 flange?
635 mm (25.00 in) per ASME B16.5.
How many bolts does a 18 inch Class 150 flange have?
16 bolts of 1-1/8 inch diameter in 1.25 inch holes on a 577.9 mm bolt circle.
What is the thickness of a 18 inch Class 150 flange?
The minimum flange thickness is 38.1 mm, including the 1.6 mm raised face.
Last updated 2026-11-02