3 inch Class 300 flange dimensions
ASME B16.5 Class 300 flange dimensions for 3 inch (DN 80) 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" (DN 80) |
| Pipe OD (bore end) | 88.9 mm |
| Flange outside diameter | 210 mm (8.27 in) |
| Minimum thickness (incl. 1.6 mm RF) | 27.0 mm (1.06 in) |
| Bolt circle diameter (PCD) | 168.3 mm (6.63 in) |
| Number of bolt holes | 8 |
| Bolt hole diameter | 0.88 in (22.4 mm) |
| Stud bolt diameter | 3/4" UNC |
| Raised face height | 1.6 mm (1/16 in) |
A complete 3" Class 300 joint needs 8 stud bolts of 3/4" diameter with 16 heavy hex nuts and one gasket.
Class 300 vs Class 150 — 3"
| Dimension | Class 300 | Class 150 |
|---|---|---|
| OD | 210 mm | 190 mm |
| Thickness | 27.0 mm | 22.3 mm |
| Bolt circle | 168.3 mm | 152.4 mm |
| Bolts | 8 × 3/4" | 4 × 5/8" |
Class 300 and Class 150 flanges do not bolt together — see 3" Class 150.
Frequently asked questions
What is the OD of a 3 inch Class 300 flange?
210 mm (8.27 in) per ASME B16.5.
How many bolts does a 3 inch Class 300 flange have?
8 bolts of 3/4 inch diameter in 0.88 inch holes on a 168.3 mm bolt circle.
What is the thickness of a 3 inch Class 300 flange?
The minimum flange thickness is 27.0 mm, including the 1.6 mm raised face.
Last updated 2026-11-02