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M4 Tap Drill Size

M4 × 0.7 is the default machine screw for electronics covers, DIN-rail gear, 3D-printer frames and small aluminium brackets. Almost every metric tap set starts here.

Recommended tap drill

3.4mm

0.1339 in

75% thread: tap drill ≈ major − pitch (4 − engagement × 1.0825 × 0.7).

Designation
M4
Major diameter
4 mm
Pitch
0.7 mm
TPI
36.286
Basic minor Ø
3.242 mm
Internal / external
Internal tap drill shown · external uses major Ø
Clearance · close
4.3 mm
Clearance · normal
4.6 mm
Clearance · loose
5.3 mm

Tap drill = 4.00 − 0.70 = 3.30 mm. Close clearance 4.3 mm, normal 4.5 mm, loose 5.0 mm. In 3D-printed plastic, heat-set M4 inserts need the insert maker’s bore, not 3.3 mm. Fine M4 × 0.5 is uncommon outside instruments.

Formula

Major Ø 4 mm

Pitch 0.7 mm

Tap drill 3.4 mm

Minor Ø 3.242 mm

M4 × 0.7 at a glance

Tap drill 3.4 mm. Close / normal / loose clearance: 4.3 / 4.6 / 5.3 mm.

Full metric and imperial charts live on the thread & tap drill calculator. Other common sizes: M8 × 1.25, M10 × 1.5, M12 × 1.75, M6 × 1, M16 × 2, M5 × 0.8, 1/4-20 UNC.

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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