Hole coordinates on a pitch circle
How to use
- Find the table for your number of holes.
- Multiply the X and Y factors by the pitch circle diameter (PCD). Coordinates are from the circle centre, with hole 1 on the +X axis and angles measured anticlockwise.
- To start with a hole somewhere else, add your start angle to every angle. Flanges are normally drilled with holes straddling the centre lines: add half the spacing.
- To check a pattern with callipers: distance between neighbouring hole centres = PCD × chord factor.
Example: 6 holes on 125 mm PCD. Hole 2: X = 0.25 × 125 = 31.25, Y = 0.43301 × 125 = 54.13 mm. Hole spacing = 125 × 0.5 = 62.5 mm.
Hole-to-hole distance
| Holes | Spacing° | Chord factor |
|---|---|---|
| 3 | 120 | 0.86603 |
| 4 | 90 | 0.70711 |
| 5 | 72 | 0.58779 |
| 6 | 60 | 0.50000 |
| 7 | 51.429 | 0.43388 |
| 8 | 45 | 0.38268 |
| 9 | 40 | 0.34202 |
| 10 | 36 | 0.30902 |
| 11 | 32.727 | 0.28173 |
| 12 | 30 | 0.25882 |
| 13 | 27.692 | 0.23932 |
| 14 | 25.714 | 0.22252 |
| 15 | 24 | 0.20791 |
| 16 | 22.5 | 0.19509 |
| 17 | 21.176 | 0.18375 |
| 18 | 20 | 0.17365 |
| 19 | 18.947 | 0.16459 |
| 20 | 18 | 0.15643 |
| 21 | 17.143 | 0.14904 |
| 22 | 16.364 | 0.14231 |
| 23 | 15.652 | 0.13617 |
| 24 | 15 | 0.13053 |
3 holes - spacing 120°
| Hole | Angle° | X × PCD | Y × PCD |
|---|---|---|---|
| 1 | 0 | +0.50000 | +0.00000 |
| 2 | 120 | -0.25000 | +0.43301 |
| 3 | 240 | -0.25000 | -0.43301 |
4 holes - spacing 90°
| Hole | Angle° | X × PCD | Y × PCD |
|---|---|---|---|
| 1 | 0 | +0.50000 | +0.00000 |
| 2 | 90 | +0.00000 | +0.50000 |
| 3 | 180 | -0.50000 | +0.00000 |
| 4 | 270 | -0.00000 | -0.50000 |
5 holes - spacing 72°
| Hole | Angle° | X × PCD | Y × PCD |
|---|---|---|---|
| 1 | 0 | +0.50000 | +0.00000 |
| 2 | 72 | +0.15451 | +0.47553 |
| 3 | 144 | -0.40451 | +0.29389 |
| 4 | 216 | -0.40451 | -0.29389 |
| 5 | 288 | +0.15451 | -0.47553 |
6 holes - spacing 60°
| Hole | Angle° | X × PCD | Y × PCD |
|---|---|---|---|
| 1 | 0 | +0.50000 | +0.00000 |
| 2 | 60 | +0.25000 | +0.43301 |
| 3 | 120 | -0.25000 | +0.43301 |
| 4 | 180 | -0.50000 | +0.00000 |
| 5 | 240 | -0.25000 | -0.43301 |
| 6 | 300 | +0.25000 | -0.43301 |
7 holes - spacing 51.429°
| Hole | Angle° | X × PCD | Y × PCD |
|---|---|---|---|
| 1 | 0 | +0.50000 | +0.00000 |
| 2 | 51.43 | +0.31174 | +0.39092 |
| 3 | 102.86 | -0.11126 | +0.48746 |
| 4 | 154.29 | -0.45048 | +0.21694 |
| 5 | 205.71 | -0.45048 | -0.21694 |
| 6 | 257.14 | -0.11126 | -0.48746 |
| 7 | 308.57 | +0.31174 | -0.39092 |
8 holes - spacing 45°
| Hole | Angle° | X × PCD | Y × PCD |
|---|---|---|---|
| 1 | 0 | +0.50000 | +0.00000 |
| 2 | 45 | +0.35355 | +0.35355 |
| 3 | 90 | +0.00000 | +0.50000 |
| 4 | 135 | -0.35355 | +0.35355 |
| 5 | 180 | -0.50000 | +0.00000 |
| 6 | 225 | -0.35355 | -0.35355 |
| 7 | 270 | -0.00000 | -0.50000 |
| 8 | 315 | +0.35355 | -0.35355 |
9 holes - spacing 40°
| Hole | Angle° | X × PCD | Y × PCD |
|---|---|---|---|
| 1 | 0 | +0.50000 | +0.00000 |
| 2 | 40 | +0.38302 | +0.32139 |
| 3 | 80 | +0.08682 | +0.49240 |
| 4 | 120 | -0.25000 | +0.43301 |
| 5 | 160 | -0.46985 | +0.17101 |
| 6 | 200 | -0.46985 | -0.17101 |
| 7 | 240 | -0.25000 | -0.43301 |
| 8 | 280 | +0.08682 | -0.49240 |
| 9 | 320 | +0.38302 | -0.32139 |
10 holes - spacing 36°
| Hole | Angle° | X × PCD | Y × PCD |
|---|---|---|---|
| 1 | 0 | +0.50000 | +0.00000 |
| 2 | 36 | +0.40451 | +0.29389 |
| 3 | 72 | +0.15451 | +0.47553 |
| 4 | 108 | -0.15451 | +0.47553 |
| 5 | 144 | -0.40451 | +0.29389 |
| 6 | 180 | -0.50000 | +0.00000 |
| 7 | 216 | -0.40451 | -0.29389 |
| 8 | 252 | -0.15451 | -0.47553 |
| 9 | 288 | +0.15451 | -0.47553 |
| 10 | 324 | +0.40451 | -0.29389 |
11 holes - spacing 32.727°
| Hole | Angle° | X × PCD | Y × PCD |
|---|---|---|---|
| 1 | 0 | +0.50000 | +0.00000 |
| 2 | 32.73 | +0.42063 | +0.27032 |
| 3 | 65.45 | +0.20771 | +0.45482 |
| 4 | 98.18 | -0.07116 | +0.49491 |
| 5 | 130.91 | -0.32743 | +0.37787 |
| 6 | 163.64 | -0.47975 | +0.14087 |
| 7 | 196.36 | -0.47975 | -0.14087 |
| 8 | 229.09 | -0.32743 | -0.37787 |
| 9 | 261.82 | -0.07116 | -0.49491 |
| 10 | 294.55 | +0.20771 | -0.45482 |
| 11 | 327.27 | +0.42063 | -0.27032 |
12 holes - spacing 30°
| Hole | Angle° | X × PCD | Y × PCD |
|---|---|---|---|
| 1 | 0 | +0.50000 | +0.00000 |
| 2 | 30 | +0.43301 | +0.25000 |
| 3 | 60 | +0.25000 | +0.43301 |
| 4 | 90 | +0.00000 | +0.50000 |
| 5 | 120 | -0.25000 | +0.43301 |
| 6 | 150 | -0.43301 | +0.25000 |
| 7 | 180 | -0.50000 | +0.00000 |
| 8 | 210 | -0.43301 | -0.25000 |
| 9 | 240 | -0.25000 | -0.43301 |
| 10 | 270 | -0.00000 | -0.50000 |
| 11 | 300 | +0.25000 | -0.43301 |
| 12 | 330 | +0.43301 | -0.25000 |
Flange drilling
ASME B16.5 Class 150 flanges
| NPS | OD in | OD mm | PCD in | PCD mm | Holes | Hole in | Bolt |
|---|---|---|---|---|---|---|---|
| 1/2" | 3.5 | 89 | 2.38 | 60.5 | 4 | 0.62 | 1/2" |
| 3/4" | 3.88 | 99 | 2.75 | 69.8 | 4 | 0.62 | 1/2" |
| 1" | 4.25 | 108 | 3.12 | 79.2 | 4 | 0.62 | 1/2" |
| 1-1/4" | 4.62 | 117 | 3.5 | 88.9 | 4 | 0.62 | 1/2" |
| 1-1/2" | 5 | 127 | 3.88 | 98.6 | 4 | 0.62 | 1/2" |
| 2" | 6 | 152 | 4.75 | 120.6 | 4 | 0.75 | 5/8" |
| 2-1/2" | 7 | 178 | 5.5 | 139.7 | 4 | 0.75 | 5/8" |
| 3" | 7.5 | 190 | 6 | 152.4 | 4 | 0.75 | 5/8" |
| 4" | 9 | 229 | 7.5 | 190.5 | 8 | 0.75 | 5/8" |
| 5" | 10 | 254 | 8.5 | 215.9 | 8 | 0.88 | 3/4" |
| 6" | 11 | 279 | 9.5 | 241.3 | 8 | 0.88 | 3/4" |
| 8" | 13.5 | 343 | 11.75 | 298.4 | 8 | 0.88 | 3/4" |
| 10" | 16 | 406 | 14.25 | 361.9 | 12 | 1 | 7/8" |
| 12" | 19 | 483 | 17 | 431.8 | 12 | 1 | 7/8" |
EN 1092-1 PN16 flanges
| Size | OD mm | PCD mm | Holes | Hole mm | Bolt |
|---|---|---|---|---|---|
| DN15 | 95 | 65 | 4 | 14 | M12 |
| DN20 | 105 | 75 | 4 | 14 | M12 |
| DN25 | 115 | 85 | 4 | 14 | M12 |
| DN32 | 140 | 100 | 4 | 18 | M16 |
| DN40 | 150 | 110 | 4 | 18 | M16 |
| DN50 | 165 | 125 | 4 | 18 | M16 |
| DN65 | 185 | 145 | 8 | 18 | M16 |
| DN80 | 200 | 160 | 8 | 18 | M16 |
| DN100 | 220 | 180 | 8 | 18 | M16 |
| DN125 | 250 | 210 | 8 | 18 | M16 |
| DN150 | 285 | 240 | 8 | 22 | M20 |
| DN200 | 340 | 295 | 12 | 22 | M20 |
| DN250 | 405 | 355 | 12 | 26 | M24 |
| DN300 | 460 | 410 | 12 | 26 | M24 |
PN16 DN65 is 8 holes as standard; 4-hole flanges are also made by agreement (and in cast iron). Class 150 and PN16 flanges do not mate: always check OD, PCD and hole count before ordering gaskets or mating flanges.