ASME B16.5 Class 300 flange dimensions
Dimensions of ASME B16.5 Class 300 flanges in millimetres: outside diameter, minimum flange thickness, bolt circle diameter, number and size of bolt holes. Values apply to weld neck, slip-on, blind, socket weld, threaded and lap joint flanges of the same class.
| NPS | Flange OD | Thickness (min) | Bolt circle | No. of bolts | Hole dia (in) | Bolt dia (in) |
|---|---|---|---|---|---|---|
| 1/2" | 95.00 | 12.70 | 66.70 | 4 | 0.62 | 1/2 |
| 3/4" | 115.00 | 14.30 | 82.60 | 4 | 0.75 | 5/8 |
| 1" | 125.00 | 15.90 | 88.90 | 4 | 0.75 | 5/8 |
| 1-1/4" | 135.00 | 17.50 | 98.40 | 4 | 0.75 | 5/8 |
| 1-1/2" | 155.00 | 19.10 | 114.30 | 4 | 0.88 | 3/4 |
| 2" | 165.00 | 20.70 | 127.00 | 8 | 0.75 | 5/8 |
| 2-1/2" | 190.00 | 23.90 | 149.20 | 8 | 0.88 | 3/4 |
| 3" | 210.00 | 27.00 | 168.30 | 8 | 0.88 | 3/4 |
| 3-1/2" | 230.00 | 28.60 | 184.20 | 8 | 0.88 | 3/4 |
| 4" | 255.00 | 30.20 | 200.00 | 8 | 0.88 | 3/4 |
| 5" | 280.00 | 33.40 | 235.00 | 8 | 0.88 | 3/4 |
| 6" | 320.00 | 35.00 | 269.90 | 12 | 0.88 | 3/4 |
| 8" | 380.00 | 39.70 | 330.20 | 12 | 1.00 | 7/8 |
| 10" | 445.00 | 46.10 | 387.40 | 16 | 1.12 | 1 |
| 12" | 520.00 | 49.30 | 450.80 | 16 | 1.25 | 1-1/8 |
| 14" | 585.00 | 52.40 | 514.40 | 20 | 1.25 | 1-1/8 |
| 16" | 650.00 | 55.60 | 571.50 | 20 | 1.38 | 1-1/4 |
| 18" | 710.00 | 58.80 | 628.60 | 24 | 1.38 | 1-1/4 |
| 20" | 775.00 | 62.00 | 685.80 | 24 | 1.38 | 1-1/4 |
| 24" | 915.00 | 68.30 | 812.80 | 24 | 1.62 | 1-1/2 |
For Class 150 and 300 the listed thickness includes the 1.6 mm raised face (for Class 400 and above the 6.4 mm raised face is additional). Open any size for a full page. Also see Class 150 flange dimensions.
About ASME B16.5 Class 300
ASME B16.5 covers pipe flanges and flanged fittings from NPS ½ through 24. The pressure class sets the pressure–temperature rating for each material group, while bolting dimensions within a class are the same for every flange type, so a weld neck and a blind flange of the same size and class mate together. Above NPS 24 use ASME B16.47 Series A or B.
Frequently asked questions
What is the bolt circle of a 4 inch Class 300 flange?
It is 200.0 mm with 8 bolts of 3/4 inch diameter.
Does the Class 300 flange thickness include the raised face?
Yes. For Class 150 and 300, ASME B16.5 includes the 1.6 mm (1/16 in) raised face in the minimum flange thickness. For Class 400 and above the 6.4 mm raised face is added on top.
Which flange standard covers sizes above 24 inch?
ASME B16.47 Series A (MSS SP-44) and Series B (API 605) cover NPS 26 to 60.
Last updated 2026-11-02