18 inch Class 300 flange dimensions
ASME B16.5 Class 300 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 | 710 mm (27.95 in) |
| Minimum thickness (incl. 1.6 mm RF) | 58.8 mm (2.31 in) |
| Bolt circle diameter (PCD) | 628.6 mm (24.75 in) |
| Number of bolt holes | 24 |
| Bolt hole diameter | 1.38 in (35.1 mm) |
| Stud bolt diameter | 1-1/4" UNC |
| Raised face height | 1.6 mm (1/16 in) |
A complete 18" Class 300 joint needs 24 stud bolts of 1-1/4" diameter with 48 heavy hex nuts and one gasket.
Class 300 vs Class 150 — 18"
| Dimension | Class 300 | Class 150 |
|---|---|---|
| OD | 710 mm | 635 mm |
| Thickness | 58.8 mm | 38.1 mm |
| Bolt circle | 628.6 mm | 577.9 mm |
| Bolts | 24 × 1-1/4" | 16 × 1-1/8" |
Class 300 and Class 150 flanges do not bolt together — see 18" Class 150.
Frequently asked questions
What is the OD of a 18 inch Class 300 flange?
710 mm (27.95 in) per ASME B16.5.
How many bolts does a 18 inch Class 300 flange have?
24 bolts of 1-1/4 inch diameter in 1.38 inch holes on a 628.6 mm bolt circle.
What is the thickness of a 18 inch Class 300 flange?
The minimum flange thickness is 58.8 mm, including the 1.6 mm raised face.
Last updated 2026-11-02