Bolt Circle Generator
Hole positions on a pitch circle, with coordinates and a cut file.
0° is to the right, measured anticlockwise.
0 to skip.
0 for holes only, no outline.
How it works
Holes on a bolt circle sit at equal angles around a pitch circle. The angular step is 360 divided by the count, and each hole is at
x = r cos(theta), y = r sin(theta)
measured from the centre, where r is half the pitch circle diameter.
The number that gets checked on a real part is the chord — the straight-line distance between adjacent holes, which is 2r sin(180/n). That is what a caliper measures between two holes, and it is how you verify a pattern you did not draw: measure the chord and the count, and the pitch circle follows.
Clearance matters as much as position. A 6 mm bolt wants a 6.5 mm hole for a normal fit, 6.6 for a coarse one. Drilling to nominal leaves nothing for alignment error and a flange with six holes accumulates it.
Common questions
What is PCD?
Pitch circle diameter — the diameter of the circle the hole centres sit on, not the holes themselves. A wheel described as 5x114.3 has five holes on a 114.3 mm pitch circle.
How do I measure the PCD of an existing part?
For an even count, measure centre to centre across two opposite holes. For an odd count, measure the chord between adjacent holes and divide by sin(180/n) to get the diameter. The table below gives you both.
Which hole size for an M6 bolt?
6.5 mm for a close fit, 6.6 for normal, 7 for coarse — those are the ISO 273 clearance grades. Going tighter than 6.4 mm means the bolt will not drop through unless everything is perfect.