M12x1.25 tap drill size
The tap drill for an M12 × 1.25 metric fine thread is 10.8 mm (0.4252 in). It leaves about 74 % thread, the normal range for steel.
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Each option redraws the section above with the thread it would leave.
M12x1.25 thread data
- Thread
- M12 × 1.25 fine
- Pitch
- 1.25 mm 20.3 TPI
- Tap drill
- 10.8 mm
- In inches
- 0.4252"
- Thread engagement
- 74 %
- Bolt torque, 8.8 dry
- 88 N·m
- Other pitches
- M12 × 1.75 M12 × 1.5
Clearance holes for M12
ISO 273 clearance holes. The dashed circle is the M12 bolt at the same scale.
How much thread you need
Thread percentage to aim for by material.
Bars run from 50 % to 90 % thread. Typical shop practice for cut taps. Harder, tougher materials take less thread to save the tap; soft materials need more engagement to hold.
How the percentage is worked out
- D
- 12 mm, major diameter
- drill
- 10.8 mm
- P
- 1.25 mm pitch
Why not 100 %?
Going from 75 % to 100 % thread adds only about 5 % strength but roughly triples the torque needed to turn the tap. That is why the standard drill leaves 70–80 %.
For cut taps the quick rule is drill = major diameter − pitch. Form (roll) taps displace metal instead of cutting it and need a larger hole, roughly D − 0.5 P; check the tap maker's chart.
Other metric fine threads
Common questions
What size drill for an M12 × 1.25 tap?
Use a 10.8 mm drill. It leaves about 74 % thread engagement.
What is 10.8 mm in inches?
10.8 mm is 0.4252 inch.
What size clearance hole for M12?
ISO 273 gives 13 mm for a close fit, 13.5 mm normal and 14.5 mm loose.
How tight should an M12 bolt be?
About 88 N·m for class 8.8 with dry threads.