M2.2 thread data
| Major diameter D | 2.2 mm |
| Pitch P | 0.45 mm · coarse pitch |
| Pitch diameter D2 | 1.908 mm |
| Minor diameter D1 (basic profile) | 1.713 mm |
| Thread engagement H1 | 0.244 mm |
| Cutting tap drill | 1.75 mm |
| Forming tap drill, indicative range | 2.01 – 2.04 mm |
| OSG 6HX | 2.01 – 2.04 mm |
| OSG 6GX | 2.02 – 2.06 mm |
Why a forming tap needs a larger hole
A cutting tap removes material as chips, so the hole starts close to the minor diameter: 1.75 mm here. A forming tap does not cut: it displaces the material and pushes it up to form the thread crest. That is why the hole is larger, from 2.01 mm up: 0.26 mm more than for cutting. With the cutting drill, a forming tap would jam or break.
Where to sit within the range
Towards the minimum (2.01 mm) the thread is fuller, but the torque on the tap rises. Towards the maximum (2.04 mm) the tap runs lighter, but the crest stays more open. The right point depends on the tap and the material and comes from the manufacturer's catalogue. With forming taps every hundredth counts: use a good drill and check the hole.
Small sizes
Below M3 the tap is slender and breaks easily: a tight or crooked hole is enough. Forming helps here, because there are no chips to pack, but the drill size must be held precisely.
Forming tap drills: indicative range from a single source: OSG, forming taps guide to tap drill sizes (class 6HX). Basic profile to ISO 68-1. Indicative values: the catalogue of the tap you use is what counts.