Holes & threads
Drilling data, tap drills, tapping, thread milling, and countersinks.
In short: Holes & threads
These calculators provide tap drill diameters, cutting data for drilling, reaming, tapping and thread milling, countersinks, drilling depths, thread engagement lengths and tightening torques. Thread dimensions follow the standards for ISO metric threads. Engagement length and torque are simplified estimates based on VDI 2230; safety-relevant joints need a full design calculation.
Frequently asked questions about Holes & threads
Which tap drill does a metric thread need?
For metric coarse threads, tap drill diameter ≈ nominal diameter − pitch. That gives 6.8 mm for M8 × 1.25 and 10.2 mm for M12 × 1.75. Forming taps need a larger hole; use the tool manufacturer's data for them.
How deep must a screw be engaged at least?
Rules of thumb for the minimum engagement are about 1 × d in steel, about 1.25 × d in grey cast iron and about 2 × d in aluminium alloys. The actual requirement depends on the screw's property class and the strength of the internal thread; the calculator estimates it from the screw force and the permissible thread shear stress.
When is thread milling better than tapping?
Thread milling pays off for large or expensive parts, hard materials and large diameters: one cutter covers several diameters of the same pitch, the thread size can be corrected through the radius, and a broken tool rarely stays stuck in the part. Tapping is usually faster for small threads and series production.
What does a position tolerance on holes mean?
A position tolerance according to ISO 1101 limits the hole axis to a cylindrical zone around the theoretically exact position. If a hole deviates by x and y, the position deviation is 2 × √(x² + y²); this value must be smaller than the diameter of the tolerance zone.