Thread Calculator — Metric Thread Dimensions for 3D Printing

ISO Metric Thread Formulas

• Thread height H = Pitch x sqrt(3) / 2 (ISO 68-1 fundamental triangle, 60 degree form)
• Thread depth = 5H / 8 (default 0.625, adjustable in Advanced)
• Minor diameter = Major diameter - 2 x Thread depth (this gives the basic internal/nut minor D1, e.g. 6.65mm for M8, 2.46mm for M3)
• Design major = Nominal major +/- full printer tolerance
• Design minor = Nominal minor +/- (printer tolerance x minor tolerance factor)

The pitch values are ISO 261 coarse-series (M3 0.5, M4 0.7, M5 0.8, M6 1.0, M8 1.25, M10 1.5, M12 1.75 mm) and the thread depth follows ISO 68-1. The clearance offset, however, is an empirical FDM allowance — it is NOT part of ISO 724. External threads (printed bolts) come out oversize, so the major is reduced by the full printer tolerance to let them fit standard nuts; internal threads (printed holes) come out undersize, so the major is enlarged. The minor diameter receives only a fraction of that tolerance (default 0.5) because the root is less affected by the printing over/undersize than the crest. Calibrate the printer tolerance with a test print before relying on the dimensions, and print thread axes vertically (along Z) for the strongest engagement.