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BreakingChips

ISO metric · fine

M2.5 × 0.35 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

2.2 mm

0.0866" · 66% thread

Form tap

2.3 mm

0.0906" · 84% thread

Open M2.5 × 0.35 in the calculator

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

Thread dimensions

Major Ø
2.500 mm (0.0984")
Pitch
0.35 mm
Pitch Ø (basic)
2.273 mm (0.0895")
Minor Ø (internal, basic)
2.121 mm (0.0835")
Thread depth (internal)
0.189 mm (0.0075")

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 M2.5 × 0.35
DrillØ inØ mmThread
#44suggested0.08602.1869%
2.2 mmsuggested0.08662.2066%
#430.08902.2653%

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 M2.5 × 0.35
DrillØ inØ mmThread
2.3 mm0.09062.3084%
#420.09352.3753%

3-wire measurement

Best wire size
0.202 mm (0.0080")
Over wires, at basic pitch Ø
2.576 mm (0.1014")

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

Sources