What drill size for an M12 × 1.25 tap?

For a cutting tap, a 10.8 mm drill (M12 × 1.25, pitch 1.25 mm).

What drill size for an M12 × 1.25 forming tap?

Between 11.37 and 11.51 mm: the indicative range from the tap makers' tables. The exact value depends on the tap and the material: check the manufacturer's catalogue.

What is the pitch of M12 × 1.25?

1.25 mm, fine pitch. Pitch diameter 11.188 mm, minor diameter 10.647 mm.

M12 × 1.25 tap drill size: 10.8 mm cutting, 11.37–11.51 mm forming

Forming taps: values are indicative. Always check your own tap supplier's catalogue: each manufacturer gives its own range.

M12 × 1.25 thread data

Major diameter D	12 mm
Pitch P	1.25 mm · fine pitch
Pitch diameter D2	11.188 mm
Minor diameter D1 (basic profile)	10.647 mm
Thread engagement H1	0.677 mm
Cutting tap drill	10.8 mm
Forming tap drill, indicative range	11.37 – 11.51 mm
OSG 6HX	11.39 – 11.46 mm
Yamawa ISO2X	11.37 – 11.51 mm

Clearance hole and counterbore for an M12 screw

Clearance hole close / medium / free	13 / 13.5 / 14.5 mm
SHCS head ISO 4762: Ø × height	18 × 12 mm
Counterbore (DIN 974-1): Ø × depth	20 × 12.6 mm

The medium clearance hole (13.5 mm) is the normal one; close is used when the screw must locate better, free when hole position tolerances are wide. The counterbore sinks the socket head below the surface: the depth shown is the head height plus a small allowance; add the washer thickness if one is used.

Clearance holes to ISO 273, heads to ISO 4762, counterbores to DIN 974-1. Values checked against several published tables.

Why a forming tap needs a larger hole

A cutting tap removes material as chips, so the hole starts close to the minor diameter: 10.8 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 11.37 mm up: 0.57 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 (11.37 mm) the thread is fuller, but the torque on the tap rises. Towards the maximum (11.51 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.

Fine pitch

A fine pitch has a shallower thread, so the drill gets closer to the nominal diameter: for M12 × 1.25 the cutting tap drill is 10.8 mm. It is used for fine adjustment, thin walls or better resistance to loosening. Always read the pitch on the drawing: the same diameter has different tap drills.

Same diameter, other pitch

← M12 × 1.5 M12 × 1 →

What the makers say

For M12 × 1.25: OSG 11.39 – 11.46 mm, Yamawa 11.37 – 11.51 mm. Each maker designs the tap profile its own way, so the range shifts by a few hundredths. The range at the top runs from the lowest to the highest of these values: if you use a tap from one brand, follow that brand's catalogue.

Forming tap drills: indicative range, from the lowest to the highest value given by the tap makers (DIN 13 / ISO 965-1): OSG, forming taps guide to tap drill sizes (class 6HX); Yamawa, Quick Guide, bored hole size for thread forming (class ISO2X). Basic profile to ISO 68-1. Indicative values: the catalogue of the tap you use is what counts.

M12 × 1.25 tap drill size