Metric Tap Drill Chart

Tap drill sizes for every metric coarse thread, M1 to M64. Metric threads are written as diameter and pitch in millimetres, and each diameter has one standard coarse pitch. Each row gives the tap drill in mm and inches, the percent of thread it leaves, the drill for tough material and the form-tap hole. Sort any column, filter by size, click a row for its full page.

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33 sizes

Metric coarse tap drill sizes: size, tap drill, decimal inch, millimetres, percent of thread, hard-material drill, form-tap drill, basic minor diameter and pitch.
					tough metal		roll tap
M1 x 0.25	0.75 mm	0.0295	0.75	77.0	0.8 mm	61.6	0.9 mm	0.0287	0.25 mm
M1.2 x 0.25	0.95 mm	0.0374	0.95	77.0	1 mm	61.6	1.1 mm	0.0366	0.25 mm
M1.4 x 0.3	1.1 mm	0.0433	1.10	77.0	1.15 mm	64.2	1.25 mm	0.0423	0.3 mm
M1.6 x 0.35	1.25 mm	0.0492	1.25	77.0	1.35 mm	55.0	1.45 mm	0.0481	0.35 mm
M2 x 0.4	1.6 mm	0.063	1.60	77.0	1.7 mm	57.7	1.8 mm	0.0617	0.4 mm
M2.5 x 0.45	2.05 mm	0.0807	2.05	77.0	2.15 mm	59.9	2.3 mm	0.0793	0.45 mm
M3 x 0.5	2.5 mm	0.0984	2.50	77.0	2.6 mm	61.6	2.8 mm	0.0968	0.5 mm
M3.5 x 0.6	2.9 mm	0.1142	2.90	77.0	3 mm	64.2	3.2 mm	0.1122	0.6 mm
M4 x 0.7	3.3 mm	0.1299	3.30	77.0	3.5 mm	55.0	3.7 mm	0.1276	0.7 mm
M5 x 0.8	4.2 mm	0.1654	4.20	77.0	4.4 mm	57.7	4.6 mm	0.1628	0.8 mm
M6 x 1	5 mm	0.1969	5.00	77.0	5.2 mm	61.6	5.6 mm	0.1936	1 mm
M7 x 1	6 mm	0.2362	6.00	77.0	6.2 mm	61.6	6.6 mm	0.233	1 mm
M8 x 1.25	6.8 mm	0.2677	6.80	73.9	7 mm	61.6	7.4 mm	0.2617	1.25 mm
M10 x 1.5	8.5 mm	0.3346	8.50	77.0	8.8 mm	61.6	9.3 mm	0.3298	1.5 mm
M12 x 1.75	10.2 mm	0.4016	10.20	79.2	10.6 mm	61.6	11.2 mm	0.3979	1.75 mm
M14 x 2	12 mm	0.4724	12.00	77.0	12.4 mm	61.6	13.1 mm	0.4659	2 mm
M16 x 2	14 mm	0.5512	14.00	77.0	14.4 mm	61.6	15.1 mm	0.5447	2 mm
M18 x 2.5	15.5 mm	0.6102	15.50	77.0	16.1 mm	58.5	16.9 mm	0.6021	2.5 mm
M20 x 2.5	17.5 mm	0.689	17.50	77.0	18.1 mm	58.5	18.9 mm	0.6809	2.5 mm
M22 x 2.5	19.5 mm	0.7677	19.50	77.0	20 mm	61.6	21 mm	0.7596	2.5 mm
M24 x 3	21 mm	0.8268	21.00	77.0	21.5 mm	64.2	22.5 mm	0.817	3 mm
M27 x 3	24 mm	0.9449	24.00	77.0	24.5 mm	64.2	25.5 mm	0.9351	3 mm
M30 x 3.5	26.5 mm	1.0433	26.50	77.0	27.5 mm	55.0	28.5 mm	1.0319	3.5 mm
M33 x 3.5	29.5 mm	1.1614	29.50	77.0	30.5 mm	55.0	31.5 mm	1.150	3.5 mm
M36 x 4	32 mm	1.2598	32.00	77.0	33 mm	57.7	34 mm	1.2469	4 mm
M39 x 4	35 mm	1.378	35.00	77.0	36 mm	57.7	37 mm	1.365	4 mm
M42 x 4.5	37.5 mm	1.4764	37.50	77.0	38.5 mm	59.9	40 mm	1.4618	4.5 mm
M45 x 4.5	40.5 mm	1.5945	40.50	77.0	41.5 mm	59.9	43 mm	1.5799	4.5 mm
M48 x 5	43 mm	1.6929	43.00	77.0	44 mm	61.6	46 mm	1.6767	5 mm
M52 x 5	47 mm	1.8504	47.00	77.0	48 mm	61.6	50 mm	1.8341	5 mm
M56 x 5.5	50.5 mm	1.9882	50.50	77.0	51.5 mm	63.0	53.5 mm	1.9703	5.5 mm
M60 x 5.5	54.5 mm	2.1457	54.50	77.0	55.5 mm	63.0	57.5 mm	2.1278	5.5 mm
M64 x 6	58 mm	2.2835	58.00	77.0	59.5 mm	57.7	60 mm	2.264	6 mm

Tap a column heading to sort. Every row links to that size's full page.

Diameter minus pitch, and when it fails

The metric rule of thumb is the easiest one in the trade: drill = diameter − pitch. It lands on about 77% of thread for any coarse or fine metric size, which is on the deep side of ideal but perfectly usable.

It works cleanly when the answer is a drill that exists. M6 x 1 gives 6 − 1 = 5 mm, and that is the chart drill. M8 x 1.25 gives 8 − 1.25 = 6.75 mm, which nobody stocks, so the charts round to 6.8 mm and accept 73.9% instead. That rounding is why the percent column on this chart is not a flat 77% all the way down.

Reading a metric callout

M8 x 1.25 is an 8 mm major diameter with 1.25 mm between crests. Written as plain M8, it means the same thing, because every diameter has exactly one standard coarse pitch and that is the default. A fine thread is always written out in full: M8 x 1 is the fine version and takes a different drill, listed on the metric fine chart.

The sizes that come up most

M5 x 0.8 (4.2 mm), M6 x 1 (5 mm) and M8 x 1.25 (6.8 mm) cover most of what turns up on imported machinery, bicycles, 3D printers and flat-pack hardware. If you buy one metric tap set, make sure it covers those.

Metric and inch are not interchangeable

M6 and 1/4-20 are close enough in diameter to start in each other's holes and then bind. So are M8 and 5/16-18, and M10 and 3/8-16. Each size page lists its nearest counterpart in the other system with that warning attached, because the diameters match and the pitches never do.

Frequently asked questions

What is the tap drill size for M6?

5 mm, which leaves 77.0% of thread. M6 x 1 is the coarse pitch, and it is what an unqualified "M6" means.

Is metric tap drill size just diameter minus pitch?

As a rule of thumb, yes, and it gives about 77% of thread. M6 x 1 works out to exactly 5 mm that way. M8 x 1.25 gives 6.75 mm, which is not a drill anyone stocks, so charts use 6.8 mm instead at 73.9%.

What does M8 x 1.25 mean?

M means an ISO metric thread, 8 is the major diameter in millimetres, and 1.25 is the pitch: the distance from one thread crest to the next, also in millimetres. Inch threads are written the other way round, as diameter and threads per inch.

What is the difference between metric coarse and metric fine?

Pitch. Each metric diameter has one standard coarse pitch, which is what a bare "M8" means, plus one or more fine pitches written out in full as M8 x 1. The coarse pitches are on this chart; the fine ones are on the metric fine chart.

Can I use an inch drill for a metric tap?

Often, yes. Every row has an inch-substitute drill on its own page with the percent of thread it gives, so you can see what the swap costs before you make it. Some are close enough to be invisible; a few are not.

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