Bolt Hole Coordinates

For a bolt circle with N bolts on a PCD of diameter D, starting at angle θ₀:

Distance Between Adjacent Holes

This is the chord length between adjacent equally-spaced holes on the bolt circle.

Common Bolt Patterns

Bolts	Angle Between	Typical Use
3	120°	Small flanges, sensor mounts
4	90°	Square flanges, bearing housings
6	60°	Medium flanges, pipe flanges DN50–DN150
8	45°	Standard flanges, DN150–DN300
12	30°	Large flanges, DN300–DN600
16	22.5°	Large pressure vessel flanges
20	18°	Very large flanges, turbine casings
24	15°	Large reactor vessels

Standard Flange PCD Reference (EN 1092-1, PN16)

DN	PCD (mm)	Bolts	Bolt Size
DN25	85	4	M12
DN50	125	4	M16
DN80	160	8	M16
DN100	190	8	M16
DN150	250	8	M20
DN200	310	8 or 12	M20
DN250	370	12	M24
DN300	430	12	M24
DN400	535	16	M27
DN500	650	20	M30
DN600	770	20	M33

Tips for CNC/DRO Work

• The X,Y coordinates shown assume the center of the bolt circle is at origin (0,0)
• For CNC work, add your actual center position offset to all coordinates
• The starting angle of 0° is at the 12 o’clock position (positive Y axis)
• Angles increase clockwise (conventional for bolt patterns)
• Always verify coordinates by checking the adjacent distance matches the calculated chord length