M3 x 0.5 Tap Drill Size (2.5 mm), Clearance Hole and Depth

The tap drill for M3 x 0.5 is 2.5 mm (0.0984 in), which gives about 77% of full thread depth. The exact 75% hole is 0.0989 in (2.51 mm). The table lists every number, letter, fractional and metric drill that gives between 55% and 90% thread, so you can work from the bits you own.

Drill	Type	in	mm	Thread	Note
#41	number	0.0960	2.44	86%	deep, hard to tap
#40	number	0.0980	2.49	79%
2.5 mm	metric	0.0984	2.50	77%	chart drill
#39	number	0.0995	2.53	73%
#38	number	0.1015	2.58	65%	easier to tap
2.6 mm	metric	0.1024	2.60	62%	easier to tap
#37	number	0.1040	2.64	55%	easier to tap

Thread % = (major diameter − drill) × TPI ÷ 0.01299 (Machinery’s Handbook), for M3 x 0.5; our arithmetic. Bold = the usual chart drill. Below about 68% the tap turns more easily, which helps in stainless steel and with small taps.

About the M3 x 0.5 thread

M3 x 0.5 is the most common small metric thread. It holds circuit boards to standoffs (most hobby boards have 3.2 mm mounting holes for M3 screws), fixes 2.5 in drives, laptop parts and optical drives, and is the default fastener in desktop 3D printers, drones and RC models. It is also common on small aluminium extrusions and camera accessories.

The rule for metric coarse threads is simple: tap drill = diameter minus pitch, so M3 x 0.5 takes a 2.5 mm drill. That gives a thread a little deeper than 75%, which is fine in aluminium and mild steel. In stainless or for a small tap in a deep hole, 2.6 mm is a common, safer choice.

M3 x 0.5 thread dimensions

Dimension	Value	Also
Nominal diameter	3 mm	0.1181 in
Pitch	0.5 mm	50.80 threads per inch equivalent
Basic pitch diameter	2.675 mm	0.1053 in
Basic minor diameter (nut)	2.459 mm	0.0968 in
Tensile stress area	5.03 mm²	0.0078 in²

Basic (nominal) dimensions from the ISO 68-1 profile: d2 = d − 0.649519 P, D1 = d − 1.082532 P, As = π/4 (d − 0.938194 P)². Our arithmetic.

Clearance hole for M3

The tapped hole is in the part that holds the thread; the part being clamped gets a clearance hole the bolt passes through. For M3 a normal fit is 3.4 mm. Never drill the clearance part with the tap drill: the screw will not pass.

Fit	Drill	Diameter
Close (ISO 273 fine)	3.2 mm	0.1260 in
Normal (ISO 273 medium)	3.4 mm	0.1339 in
Loose (ISO 273 coarse)	3.6 mm	0.1417 in

From the clearance hole tables our clearance hole calculator uses.

How deep to drill a blind M3 x 0.5 hole

Part material	Full thread wanted	Drill depth (full diameter)	Depth to drill tip (118°)
Steel or cast iron (1 × diameter)	3.0 mm	6.5 mm	7.3 mm
Aluminium or brass (2 × diameter)	6.0 mm	9.5 mm	10.3 mm

Plug tap (5 tapered threads) + 2 threads of chip room below the tap + the 118° drill point. Same rules as our tapped hole depth calculator, where you can change any of them; why 1 × and 2 ×: thread engagement chart.

Wrench size and torque for M3

Hex bolt or nut: 5.5 mm wrench (ISO)
Socket head cap screw (ISO 4762): 2.5 mm hex key

Bolt grade	Dry	Lubricated
Class 8.8	1.3 N·m (1.0 ft-lb)	1.0 N·m
Class 10.9	1.9 N·m (1.4 ft-lb)	1.4 N·m
Class 12.9	2.2 N·m (1.6 ft-lb)	1.6 N·m

T = K × D × F with F = 75% of minimum proof load (ISO 898-1) and K = 0.20 dry, 0.15 lubricated: a general starting figure, not a spec. See the bolt torque chart. The maker’s torque always takes precedence.

Threads easily mistaken for M3 x 0.5

Thread	Diameter (in)	Diameter (mm)	Pitch
M3 x 0.5 (this page)	0.1181	3.00	0.5 mm (50.8 TPI)
#4-40 UNC	0.1120	2.84	40 TPI (0.64 mm)
#4-48 UNF	0.1120	2.84	48 TPI (0.53 mm)
#5-40 UNC	0.1250	3.17	40 TPI (0.64 mm)
#5-44 UNF	0.1250	3.17	44 TPI (0.58 mm)

Threads within 6% of the same diameter, from our UNC/UNF and metric charts. None of them interchange with this one.

Tips for tapping M3 x 0.5

For M3 in 3D-printed plastic, print the hole at about 2.5 to 2.8 mm and tap it, or use brass heat-set inserts sized by the insert maker.
M3 is close to #4-40 and #5-40 inch screws; check before mixing hardware.
An M3 socket head cap screw takes a 2.5 mm hex key, the same number as the tap drill, which is a handy check that you have the right screw.
Use a tap guide; M3 taps are easily broken by a slight side load.

Frequently asked questions

What size drill bit for an M3 x 0.5 tap?

2.5 mm, which gives about 77% thread. The exact 75% size is 0.0989 in (2.51 mm).

How deep should a blind M3 x 0.5 hole be?

For a full thread of 1 × diameter in steel, drill about 6.5 mm at full diameter with a plug tap, or 7.3 mm to the drill tip; in aluminium, about 9.5 mm.

What size drill for an M3 tap in inches?

The nearest inch drill to 2.5 mm is #40 (0.098 in); 3/32 in (0.094 in) is the nearest fraction but gives a deeper, harder-to-tap thread.

What clearance hole for M3?

3.2 mm for a close fit, 3.4 mm for normal (ISO 273 medium) and 3.6 mm for a loose fit.

Sources and method

Every dimension and percentage on this page is computed from the formulas listed, not copied from another chart. Values are basic (nominal); real parts are made to tolerance classes (2A/2B for inch, 6g/6H for metric).

ASME B1.1 and FED-STD-H28/2B (Unified inch), ISO 68-1 and ISO 261 (metric): basic thread profile and stress area formulas.
Machinery’s Handbook (Industrial Press): percentage-of-thread relation used by our tap drill size calculator.
ASME B94.11M twist drill series (number, letter, fractional); 0.1 mm metric drill steps.
ISO 273 metric clearance holes; inch close, normal and loose fits as published in the ASME B18.2.8 clearance classes.
SAE J429 and ISO 898-1 proof strengths; T = K × D × F torque relation (see our bolt torque chart for the full method).
Wrench and hex key sizes: ASME B18.2.1, ASME B18.3, ASME B18.6.3, ISO 4014/4017, DIN 933 and ISO 4762 values as widely published.

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Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.