3/4 inch Class 300 flange dimensions
ASME B16.5 Class 300 flange dimensions for 3/4 inch (DN 20) 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 | 3/4" (DN 20) |
| Pipe OD (bore end) | 26.7 mm |
| Flange outside diameter | 115 mm (4.53 in) |
| Minimum thickness (incl. 1.6 mm RF) | 14.3 mm (0.56 in) |
| Bolt circle diameter (PCD) | 82.6 mm (3.25 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 3/4" Class 300 joint needs 4 stud bolts of 5/8" diameter with 8 heavy hex nuts and one gasket.
Class 300 vs Class 150 — 3/4"
| Dimension | Class 300 | Class 150 |
|---|---|---|
| OD | 115 mm | 100 mm |
| Thickness | 14.3 mm | 11.2 mm |
| Bolt circle | 82.6 mm | 69.9 mm |
| Bolts | 4 × 5/8" | 4 × 1/2" |
Class 300 and Class 150 flanges do not bolt together — see 3/4" Class 150.
Frequently asked questions
What is the OD of a 3/4 inch Class 300 flange?
115 mm (4.53 in) per ASME B16.5.
How many bolts does a 3/4 inch Class 300 flange have?
4 bolts of 5/8 inch diameter in 0.75 inch holes on a 82.6 mm bolt circle.
What is the thickness of a 3/4 inch Class 300 flange?
The minimum flange thickness is 14.3 mm, including the 1.6 mm raised face.
Last updated 2026-11-02