M3 tap drill size

Drill a 2.5 mm hole (0.0984") for an M3 × 0.5 tap. That leaves about 77% thread, the standard for general-purpose tapping.

Tap drill
2.5 mm
0.0984" · 2.50 mm · 77% thread
Inch drill
#40 79% thread
Clearance (close)
3.2 mm
Heat-set insert hole
4.00 mm
Helicoil (STI) drill
3.1 mm
M3 tap drill: 2.5 mm (0.0984 in / 2.50 mm), 77% thread

M3 thread specs

SeriesISO metric coarse
Major diameter3.00 mm (0.1181")
Pitch0.5 mm (50.8 TPI)
Basic minor diameter2.46 mm (0.0968")
Common internal class6H

Every drill that works for M3

Drills from all four sets that give 50–85% thread, largest first. Lower percentages tap easier; see how much thread you need.

DrillThreadinmmSetGood for
2.65 mm54%0.10432.65Metricdeep holes only
#3755%0.10402.64Numberdeep holes only
2.6 mm62%0.10242.60Metrichard or tough metals
#3865%0.10152.58Numberhard or tough metals
2.55 mm69%0.10042.55Metrichard or tough metals
#3973%0.09952.53Numbergeneral use
2.5 mmstandard77%0.09842.50Metricgeneral use
#4079%0.09802.49Numbergeneral use
2.45 mm85%0.09652.45Metricmore torque, more broken taps

M3 clearance hole

The hole a M3 screw passes through. ISO 273 fine, medium and coarse series.

Fitmmin
Close (fine)3.2 mm0.1260
Normal (medium)3.4 mm0.1339
Loose (coarse)3.6 mm0.1417

M3 counterbore and countersink

For a socket head cap screw to sit flush, and for a flat head socket screw.

Socket head counterboreDiameterDepth
NBK6.50 mm3.30 mm
AMES6.50 mm3.00 mm

Flat head socket screw: countersink at 90° (metric screws, ISO 10642) to 6.72 mm (0.2646") across for a flush head. Inch flat heads use 82°, so don't mix countersinks.

M3 heat-set insert hole

Hole to model for a brass heat-set insert in a 3D print. Brands size their knurl differently, so use your brand’s number.

BrandHoleInsert lengthMin. wall
CNC Kitchen4.00 mm––
ruthex4.00 mm5.7 mm1.6 mm
Accu4.00 mm––
Generic (Albany County)4.00 mm––

M3 holes in a 3D print

Printed holes usually come out undersize. Model the hole at the drill size plus what your printer loses, then tap or drill to size. Why printed holes shrink.

Print a test hole, measure it with calipers, enter the difference. 0 models the nominal size.

Hole to tap
2.50 mm
Clearance hole
3.20 mm
Heat-set insert
4.00 mm

M3 thread repair (Helicoil)

Stripped M3 thread? Drill out with the STI drill, tap with a M3 × 0.5 STI tap, and fit a wire thread insert. The drill in your repair kit’s instructions wins over any chart.

ChartSTI drillinmm
MISUMI3.1 mm0.12203.10

Related sizes

M2.5next size downM4next size up4-40closest inchFull chartmetric coarse

Frequently asked questions

What size drill do I use for an M3 tap?
Use a 2.5 mm (2.50 mm / 0.0984 in) drill. It leaves about 77% thread, the standard for general-purpose tapping.
What inch drill can I use for an M3 tap?
#40 (2.49 mm / 0.0980 in) is the closest, giving about 79% thread. Anything from about 65% to 80% thread taps well in most materials.
What size clearance hole for an M3 screw?
3.2 mm (3.20 mm) for a close fit, 3.4 mm (3.40 mm) for a normal fit.
What hole size for an M3 heat-set insert?
4.0 mm in the brands listed here. Check your insert's own listing; the hole is sized for that insert's knurl.
What is the inch equivalent of M3?
4-40 is the closest size (2.84 mm vs 3.00 mm major diameter). The pitches differ, so the screws and tapped holes are not interchangeable.

Sources

Spotted a wrong number? Email contact@clove3d.com and it gets fixed.

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% thread = (major − drill) ÷ (1.299 × pitch) × 100. The standard drill comes from published charts and is checked against this formula on every build.