Skip to content
BreakingChips

ISO metric · fine

M2 × 0.25 tap drill size

For general work, OSG suggests 65–70% of full thread. Harder materials and deep holes want less; the calculator sets it from your material.

Cut tap

1.8 mm

0.0709" · 62% thread

Or #50 (0.0700") for 68%

Form tap

1.9 mm

0.0748" · 59% thread

Open M2 × 0.25 in the calculator

Pick your material for its % of thread, tapping RPM and the rigid-tap code.

Thread dimensions

Major Ø
2.000 mm (0.0787")
Pitch
0.25 mm
Pitch Ø (basic)
1.838 mm (0.0723")
Minor Ø (internal, basic)
1.729 mm (0.0681")
Thread depth (internal)
0.135 mm (0.0053")

Basic sizes of the 60° form. Tolerance classes (6H) set the limits around them.

Cut tap drills

For a cutting (fluted or spiral) tap. Every standard drill from 50% to 85% thread; suggested rows are in the 65–70% band.

Cut tap drills for M2 × 0.25
DrillØ inØ mmThread
#50suggested0.07001.7868%
1.8 mm0.07091.8062%

Form tap drills

A form (roll) tap displaces metal instead of cutting it, so it needs a bigger hole. Every standard drill from 50% to 85% thread; suggested rows are in the 65–70% band.

Form tap drills for M2 × 0.25
DrillØ inØ mmThread
1.9 mm0.07481.9059%

3-wire measurement

Best wire size
0.144 mm (0.0057")
Over wires, at basic pitch Ø
2.054 mm (0.0809")

For the external thread (the screw). The best wire touches the flanks at the pitch diameter.

Sources