75% is the usual value for steel and aluminium. Use 50–65% for hard materials (a tap needs a lot more torque above that, with little extra strength) and 80–90% for soft plastics, where a stripped thread — not a broken tap — is the real risk. Roll-form (cold-forming) taps displace metal instead of cutting it and need a larger drill than a cut tap at the same engagement — check the tap's own spec. The clearance drill is a simple rule of thumb, not an ISO 273 fit class; check the standard for a close or medium fit.

See also CNC Feeds & Speeds for spindle RPM and feed rate on the same hole, and Steps per mm for axis calibration on a 3D printer or CNC.