Flange PCD and Bolt Hole Chart
Verified by Rachel Mayfield, Supply Chain Analyst - April 2026
Flange pitch circle diameter (PCD), bolt count, hole size, and bolt spec for the two most common UK flange standards: EN 1092-1 PN 16 (metric, used for general water, building services, and chemical pipework) and ANSI B16.5 Class 150 (imperial, used for oil, gas, and imported plant). Flange PCD and Bolt Hole Chart Don't mix standards - dimensions and sealing faces differ.
EN 1092-1 PN 16 flanges (metric)
| DN | NPS | OD (mm) | PCD (mm) | Bolts | Hole Dia (mm) | Bolt Size |
|---|---|---|---|---|---|---|
| DN 15 | 1/2" | 95 | 65 | 4 | 14 | M12 |
| DN 20 | 3/4" | 105 | 75 | 4 | 14 | M12 |
| DN 25 | 1" | 115 | 85 | 4 | 14 | M12 |
| DN 32 | 1-1/4" | 140 | 100 | 4 | 18 | M16 |
| DN 40 | 1-1/2" | 150 | 110 | 4 | 18 | M16 |
| DN 50 | 2" | 165 | 125 | 4 | 18 | M16 |
| DN 65 | 2-1/2" | 185 | 145 | 4 | 18 | M16 |
| DN 80 | 3" | 200 | 160 | 8 | 18 | M16 |
| DN 100 | 4" | 220 | 180 | 8 | 18 | M16 |
| DN 125 | 5" | 250 | 210 | 8 | 18 | M16 |
| DN 150 | 6" | 285 | 240 | 8 | 22 | M20 |
| DN 200 | 8" | 340 | 295 | 12 | 22 | M20 |
| DN 250 | 10" | 405 | 355 | 12 | 26 | M24 |
| DN 300 | 12" | 460 | 410 | 12 | 26 | M24 |
| DN 350 | 14" | 520 | 470 | 16 | 26 | M24 |
| DN 400 | 16" | 580 | 525 | 16 | 30 | M27 |
| DN 500 | 20" | 715 | 650 | 20 | 33 | M30 |
ANSI B16.5 Class 150 flanges (imperial)
| NPS | OD (mm) | PCD (mm) | Bolts | Hole Dia (mm) | Bolt Size |
|---|---|---|---|---|---|
| 1/2" | 88.9 | 60.3 | 4 | 15.9 | 1/2" UNC |
| 3/4" | 98.4 | 69.9 | 4 | 15.9 | 1/2" UNC |
| 1" | 108.0 | 79.4 | 4 | 15.9 | 1/2" UNC |
| 1-1/4" | 117.5 | 88.9 | 4 | 15.9 | 1/2" UNC |
| 1-1/2" | 127.0 | 98.4 | 4 | 15.9 | 1/2" UNC |
| 2" | 152.4 | 120.7 | 4 | 19.1 | 5/8" UNC |
| 2-1/2" | 177.8 | 139.7 | 4 | 19.1 | 5/8" UNC |
| 3" | 190.5 | 152.4 | 4 | 19.1 | 5/8" UNC |
| 4" | 228.6 | 190.5 | 8 | 19.1 | 5/8" UNC |
| 5" | 254.0 | 215.9 | 8 | 22.2 | 3/4" UNC |
| 6" | 279.4 | 241.3 | 8 | 22.2 | 3/4" UNC |
| 8" | 342.9 | 298.4 | 8 | 22.2 | 3/4" UNC |
| 10" | 406.4 | 362.0 | 12 | 25.4 | 7/8" UNC |
| 12" | 482.6 | 431.8 | 12 | 25.4 | 7/8" UNC |
How to use the flange PCD chart
PCD (pitch circle diameter) is the diameter of the circle passing through the centres of the bolt holes. To mark out a flange, draw a circle at the PCD, divide by the bolt count, and centre each hole on that circle. Always keep bolt holes straddling the vertical centreline (never on it) so a flange can rotate 180 degrees and still fit.
Pressure class selection: PN 16 suits typical building services, potable water, and low-pressure industrial pipework. PN 25 and PN 40 handle higher pressures with thicker flanges but the same PCD. ANSI Class 150 corresponds roughly to PN 20, Class 300 to PN 50, and Class 600 to PN 100 - but exact matches are rare; always confirm against the specific flange standard.
Gasket selection matters as much as the flange itself. Raised-face flanges accept non-asbestos fibre gaskets. Ring-type joint (RTJ) flanges need soft metal rings. Flat-face flanges pair with full-face gaskets, typically in cast iron fittings.
Related standards
- BS EN 1092-1 - Flanges: steel flanges for pipes, valves, fittings (PN-designated)
- BS EN 1092-2 - Flanges: cast iron flanges
- BS EN 1092-3 - Flanges: copper alloy flanges
- ASME B16.5 - Pipe flanges and flanged fittings (NPS 1/2 through 24)
- ASME B16.47 - Large diameter steel flanges (NPS 26 through 60)
- BS 10 - Withdrawn UK flange standard (still referenced in older drawings)
References
- BS EN 1092-1:2018 - Steel flanges PN-designated
- ASME B16.5-2020 - Pipe flanges and flanged fittings
- British Valve and Actuator Association - UK industry reference
Frequently Asked Questions
What is the PCD of a DN 50 PN 16 flange?
A DN 50 PN 16 flange (EN 1092-1) has a PCD of 125 mm, 4 bolt holes of 18 mm diameter, outer diameter 165 mm, and uses M16 bolts. This is equivalent to a 2 inch NPS.
Are EN 1092 and ANSI B16.5 flanges interchangeable?
No. EN 1092 PN 16 and ANSI Class 150 flanges have different PCDs, different bolt sizes, and different sealing face profiles. A DN 50 PN 16 has 125 mm PCD with M16 bolts; a 2 inch ANSI Class 150 has 120.7 mm PCD with 5/8 inch UNC bolts. Never try to bolt them together - use a conversion flange or spool.
How many bolts does a DN 100 flange have?
A DN 100 PN 16 flange has 8 bolts of M16 size on a 180 mm PCD, with 18 mm diameter bolt holes. Flanges at DN 80 and above typically have 8 bolts; smaller sizes have 4.
What does the Flange PCD and Bolt Hole Chart provide information about?
The Flange PCD and Bolt Hole Chart provides details on the pitch circle diameter (PCD), number of bolts, hole size, and bolt specifications for two common UK flange standards: EN 1092-1 PN 16 (metric) and ANSI B16.5 Class 150 (imperial).
Why is it important not to mix metric and imperial flange standards according to the Flange PCD and Bolt Hole Chart?
Mixing metric and imperial flange standards can lead to incorrect dimensions and sealing issues, as they have different sizes and specifications for bolt holes and sealing faces. The Flange PCD and Bolt Hole Chart highlights these differences to prevent such errors.
How do you determine the correct PCD and bolt hole size for a DN 50 EN 1092-1 PN 16 flange using the chart?
For a DN 50 EN 1092-1 PN 16 flange, the Flange PCD and Bolt Hole Chart shows that the pitch circle diameter (PCD) is 125 mm with four bolt holes, each having a hole diameter of 18 mm. The appropriate bolt size is M16.
What are the two main types of standards covered in the Flange PCD and Bolt Hole Chart?
The Flange PCD and Bolt Hole Chart covers EN 1092-1 PN 16, a metric standard commonly used for water, building services, and chemical pipework, and ANSI B16.5 Class 150, an imperial standard typically used in oil and gas industries.
Where can UK engineers find reliable suppliers of flanges that conform to the standards listed in the Flange PCD and Bolt Hole Chart?
UK engineers can consult local industrial supply companies or online platforms specializing in piping components for reliable suppliers of EN 1092-1 PN 16 and ANSI B16.5 Class 150 flanges.
How does the cost and availability of metric vs imperial flange sizes vary according to the chart's standards?
Metric flanges like those specified in EN 1092-1 PN 16 are often more readily available and may be less expensive than ANSI B16.5 Class 150 imperial flanges, which can sometimes require special ordering due to less widespread use.
What is the PCD for a DN 80 (3") EN 1092-1 PN 16 flange according to the Flange PCD and Bolt Hole Chart?
The pitch circle diameter (PCD) for a DN 80 (3") EN 1092-1 PN 16 flange is 155 mm, with four bolt holes of 18 mm each and an M16 bolt size as specified in the Flange PCD and Bolt Hole Chart.