Metric coarse

M1 × 0.25

Tap drill 0.75 mm for a M1 × 0.25 thread — major Ø 1 mm, pitch 0.25 mm (101.6 TPI).

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Tap drill

0.75 mm

0.75 mm · ≈77% thread

Profile

Thread form & key diameters

Dimensions

Designation	M1 × 0.25
Major (outside) diameter	1 mm · 0.0394"
Pitch	0.25 mm · 101.6 TPI
Pitch diameter	0.838 mm · 0.033"
Minor diameter (external)	0.693 mm · 0.0273"
Minor diameter (internal)	0.729 mm · 0.0287"
Recommended tap drill	0.75 mm · ≈77% thread
Clearance hole	Close 1.1 · Normal 1.2 · Loose 1.3 mm

ISO 273 clearance holes (fine / medium / coarse).

What tap drill do I need for M1 × 0.25?

For a M1 × 0.25 thread, drill the hole with a 0.75 mm tap drill (0.75 mm — the standard D − P rule) before tapping. That produces roughly 77% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 1 mm and a pitch of 0.25 mm (101.6 TPI).

To pass a M1 × 0.25 bolt through a part rather than thread it, use a clearance hole: Close 1.1 · Normal 1.2 · Loose 1.3 mm.

All values are generated from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables — not hand-entered. See the full reference.

Nearby sizes

More metric coarse threads

M1.2 × 0.25Tap 0.95 mmØ 1.2 mm · pitch 0.25 mm M1.4 × 0.3Tap 1.1 mmØ 1.4 mm · pitch 0.3 mm M1.6 × 0.35Tap 1.25 mmØ 1.6 mm · pitch 0.35 mm M1.8 × 0.35Tap 1.45 mmØ 1.8 mm · pitch 0.35 mm M2 × 0.4Tap 1.6 mmØ 2 mm · pitch 0.4 mm M2.5 × 0.45Tap 2.05 mmØ 2.5 mm · pitch 0.45 mm M3 × 0.5Tap 2.5 mmØ 3 mm · pitch 0.5 mm M3.5 × 0.6Tap 2.9 mmØ 3.5 mm · pitch 0.6 mm