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M12 Thread & Tap Drill

M12 coarse (M12 × 1.75) is widely used for engine mounts, structural joints and hydraulic flanges. Fine M12 × 1.5 / 1.25 / 1 pitches are common on OEM equipment.

Recommended tap drill

10.6mm

0.4173 in

75% thread: tap drill ≈ major − pitch (12 − engagement × 1.0825 × 1.75).

Designation
M12
Major diameter
12 mm
Pitch
1.75 mm
TPI
14.514
Basic minor Ø
10.106 mm
Internal / external
Internal tap drill shown · external uses major Ø
Clearance · close
12.4 mm
Clearance · normal
13 mm
Clearance · loose
14 mm

Tap drill ≈ 12.00 − 1.75 = 10.25 mm, issued as 10.2 mm. Fine M12 × 1.5 taps with 10.5 mm; M12 × 1.25 with 10.8 mm. Normal clearance is 13.5 mm. Always match the pitch stamped on the bolt — mixing 1.75 and 1.5 will destroy both parts.

Formula

Major Ø 12 mm

Pitch 1.75 mm

Tap drill 10.6 mm

Minor Ø 10.106 mm

M12 × 1.75 at a glance

Tap drill 10.6 mm. Close / normal / loose clearance: 12.4 / 13 / 14 mm.

Full metric and imperial charts live on the thread & tap drill calculator. Other common sizes: M8 × 1.25, M10 × 1.5, M6 × 1, M16 × 2.

Frequently asked questions

How is a metric tap drill size determined?+

For a typical 75% thread engagement, tap drill ≈ major diameter − pitch. For M8 × 1.25 that is 8.00 − 1.25 = 6.75 mm, rounded to the standard 6.8 mm drill. Fine pitches subtract a smaller pitch and therefore use a larger drill.

What is the difference between tap drill and clearance drill?+

A tap drill is the hole you tap (internal thread). A clearance drill is a through-hole for a bolt to pass freely. Clearance holes are given as close, normal and loose fits per common workshop practice (aligned with ISO 273 medium series).

Do you support imperial threads?+

Yes. UNC, UNF, UNEF, BSW and BSF are included with TPI, major diameter, tap drill (inch and nearest fractional), and clearance drill recommendations.

Is 75% thread always correct?+

75% is the usual workshop target for strength versus tapping torque. Softer materials or difficult holes sometimes use 60–70%; high-strength joints in steel may go higher. The calculator shows the 75% recommendation and the formula so you can adjust.

What does M8 × 1.25 mean?+

M8 is a metric thread with 8 mm major diameter. 1.25 mm is the pitch (distance between crests) — the ISO coarse pitch for M8. Fine M8 variants include 1.0 mm and 0.75 mm pitch.

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