Tap Drill Size Chart

Clearance Hole Chart

Clearance hole sizes for every inch and metric thread in this chart. A clearance hole is the through hole the bolt passes in, not a tapped hole, so it is always larger than the thread. Inch sizes follow ASME B18.2.8 and metric sizes ISO 273. Sort any column, filter by size, and click a row for that size's full page.

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124 sizes

Clearance hole sizes by thread: size, the standard the row follows, and the close/fine, normal/medium and loose/coarse hole in inches and millimetres.
ISO: fine ISO: medium
M1 x 0.25 1.1 mm 0.0433 / 1.1 1.2 mm 0.0472 / 1.2
M1.2 x 0.25 1.3 mm 0.0512 / 1.3 1.4 mm 0.0551 / 1.4
M1.4 x 0.3 1.5 mm 0.0591 / 1.5 1.6 mm 0.063 / 1.6
#0-80 #51 0.067 / 1.7 #48 0.076 / 1.93
M1.6 x 0.35 1.7 mm 0.0669 / 1.7 1.8 mm 0.0709 / 1.8
#1-64 #46 0.081 / 2.06 #43 0.089 / 2.26
#1-72 #46 0.081 / 2.06 #43 0.089 / 2.26
M2 x 0.4 2.2 mm 0.0866 / 2.2 2.4 mm 0.0945 / 2.4
#2-56 3/32″ 0.0938 / 2.38 #38 0.1015 / 2.58
#2-64 3/32″ 0.0938 / 2.38 #38 0.1015 / 2.58
M2.5 x 0.45 2.7 mm 0.1063 / 2.7 2.9 mm 0.1142 / 2.9
#3-48 #36 0.1065 / 2.71 #32 0.116 / 2.95
#3-56 #36 0.1065 / 2.71 #32 0.116 / 2.95
#4-40 #31 0.120 / 3.05 #30 0.1285 / 3.26
#4-48 #31 0.120 / 3.05 #30 0.1285 / 3.26
M3 x 0.5 3.2 mm 0.126 / 3.2 3.4 mm 0.1339 / 3.4
#5-40 9/64″ 0.1406 / 3.57 5/32″ 0.1562 / 3.97
#5-44 9/64″ 0.1406 / 3.57 5/32″ 0.1562 / 3.97
M3.5 x 0.6 3.7 mm 0.1457 / 3.7 3.9 mm 0.1535 / 3.9
#6-32 #23 0.154 / 3.91 #18 0.1695 / 4.31
#6-40 #23 0.154 / 3.91 #18 0.1695 / 4.31
M4 x 0.7 4.3 mm 0.1693 / 4.3 4.5 mm 0.1772 / 4.5
#8-32 #15 0.180 / 4.57 #9 0.196 / 4.98
#8-36 #15 0.180 / 4.57 #9 0.196 / 4.98
#10-24 #5 0.2055 / 5.22 #2 0.221 / 5.61
#10-32 #5 0.2055 / 5.22 #2 0.221 / 5.61
M5 x 0.8 5.3 mm 0.2087 / 5.3 5.5 mm 0.2165 / 5.5
#12-24 — — — —
#12-28 — — — —
#12-32 — — — —
M6 x 1 6.4 mm 0.252 / 6.4 6.6 mm 0.2598 / 6.6
1/4-20 17/64″ 0.2656 / 6.75 9/32″ 0.2812 / 7.14
1/4-28 17/64″ 0.2656 / 6.75 9/32″ 0.2812 / 7.14
1/4-32 17/64″ 0.2656 / 6.75 9/32″ 0.2812 / 7.14
M7 x 1 7.4 mm 0.2913 / 7.4 7.6 mm 0.2992 / 7.6
5/16-18 21/64″ 0.3281 / 8.33 11/32″ 0.3438 / 8.73
5/16-24 21/64″ 0.3281 / 8.33 11/32″ 0.3438 / 8.73
5/16-32 21/64″ 0.3281 / 8.33 11/32″ 0.3438 / 8.73
M8 x 1.25 8.4 mm 0.3307 / 8.4 9 mm 0.3543 / 9
M8 x 1 8.4 mm 0.3307 / 8.4 9 mm 0.3543 / 9
M8 x 0.75 8.4 mm 0.3307 / 8.4 9 mm 0.3543 / 9
3/8-16 25/64″ 0.3906 / 9.92 13/32″ 0.4062 / 10.32
3/8-24 25/64″ 0.3906 / 9.92 13/32″ 0.4062 / 10.32
3/8-32 25/64″ 0.3906 / 9.92 13/32″ 0.4062 / 10.32
M10 x 1.5 10.5 mm 0.4134 / 10.5 11 mm 0.4331 / 11
M10 x 1.25 10.5 mm 0.4134 / 10.5 11 mm 0.4331 / 11
M10 x 1 10.5 mm 0.4134 / 10.5 11 mm 0.4331 / 11
M10 x 0.75 10.5 mm 0.4134 / 10.5 11 mm 0.4331 / 11
7/16-14 29/64″ 0.4531 / 11.51 15/32″ 0.4688 / 11.91
7/16-20 29/64″ 0.4531 / 11.51 15/32″ 0.4688 / 11.91
7/16-28 29/64″ 0.4531 / 11.51 15/32″ 0.4688 / 11.91
M12 x 1.75 13 mm 0.5118 / 13 13.5 mm 0.5315 / 13.5
M12 x 1.5 13 mm 0.5118 / 13 13.5 mm 0.5315 / 13.5
M12 x 1.25 13 mm 0.5118 / 13 13.5 mm 0.5315 / 13.5
M12 x 1 13 mm 0.5118 / 13 13.5 mm 0.5315 / 13.5
1/2-13 17/32″ 0.5312 / 13.49 9/16″ 0.5625 / 14.29
1/2-20 17/32″ 0.5312 / 13.49 9/16″ 0.5625 / 14.29
1/2-28 17/32″ 0.5312 / 13.49 9/16″ 0.5625 / 14.29
M14 x 2 15 mm 0.5906 / 15 15.5 mm 0.6102 / 15.5
M14 x 1.5 15 mm 0.5906 / 15 15.5 mm 0.6102 / 15.5
M14 x 1.25 15 mm 0.5906 / 15 15.5 mm 0.6102 / 15.5
9/16-12 — — — —
9/16-18 — — — —
9/16-24 — — — —
5/8-11 21/32″ 0.6562 / 16.67 11/16″ 0.6875 / 17.46
5/8-18 21/32″ 0.6562 / 16.67 11/16″ 0.6875 / 17.46
5/8-24 21/32″ 0.6562 / 16.67 11/16″ 0.6875 / 17.46
M16 x 2 17 mm 0.6693 / 17 17.5 mm 0.689 / 17.5
M16 x 1.5 17 mm 0.6693 / 17 17.5 mm 0.689 / 17.5
M16 x 1 17 mm 0.6693 / 17 17.5 mm 0.689 / 17.5
M18 x 2.5 19 mm 0.748 / 19 20 mm 0.7874 / 20
M18 x 2 19 mm 0.748 / 19 20 mm 0.7874 / 20
M18 x 1.5 19 mm 0.748 / 19 20 mm 0.7874 / 20
M18 x 1 19 mm 0.748 / 19 20 mm 0.7874 / 20
3/4-10 25/32″ 0.7812 / 19.84 13/16″ 0.8125 / 20.64
3/4-16 25/32″ 0.7812 / 19.84 13/16″ 0.8125 / 20.64
3/4-20 25/32″ 0.7812 / 19.84 13/16″ 0.8125 / 20.64
M20 x 2.5 21 mm 0.8268 / 21 22 mm 0.8661 / 22
M20 x 2 21 mm 0.8268 / 21 22 mm 0.8661 / 22
M20 x 1.5 21 mm 0.8268 / 21 22 mm 0.8661 / 22
M20 x 1 21 mm 0.8268 / 21 22 mm 0.8661 / 22
M22 x 2.5 23 mm 0.9055 / 23 24 mm 0.9449 / 24
M22 x 2 23 mm 0.9055 / 23 24 mm 0.9449 / 24
M22 x 1.5 23 mm 0.9055 / 23 24 mm 0.9449 / 24
7/8-9 29/32″ 0.9062 / 23.02 15/16″ 0.9375 / 23.81
7/8-14 29/32″ 0.9062 / 23.02 15/16″ 0.9375 / 23.81
7/8-20 29/32″ 0.9062 / 23.02 15/16″ 0.9375 / 23.81
M24 x 3 25 mm 0.9843 / 25 26 mm 1.0236 / 26
M24 x 2 25 mm 0.9843 / 25 26 mm 1.0236 / 26
M24 x 1.5 25 mm 0.9843 / 25 26 mm 1.0236 / 26
1-8 1-1/32″ 1.0312 / 26.19 1-3/32″ 1.0938 / 27.78
1-12 1-1/32″ 1.0312 / 26.19 1-3/32″ 1.0938 / 27.78
1-20 1-1/32″ 1.0312 / 26.19 1-3/32″ 1.0938 / 27.78
M27 x 3 28 mm 1.1024 / 28 30 mm 1.1811 / 30
M27 x 2 28 mm 1.1024 / 28 30 mm 1.1811 / 30
M27 x 1.5 28 mm 1.1024 / 28 30 mm 1.1811 / 30
1-1/8-7 1-5/32″ 1.1562 / 29.37 1-7/32″ 1.2188 / 30.96
1-1/8-12 1-5/32″ 1.1562 / 29.37 1-7/32″ 1.2188 / 30.96
M30 x 3.5 31 mm 1.2205 / 31 33 mm 1.2992 / 33
M30 x 2 31 mm 1.2205 / 31 33 mm 1.2992 / 33
M30 x 1.5 31 mm 1.2205 / 31 33 mm 1.2992 / 33
1-1/4-7 1-9/32″ 1.2812 / 32.54 1-11/32″ 1.3438 / 34.13
1-1/4-12 1-9/32″ 1.2812 / 32.54 1-11/32″ 1.3438 / 34.13
M33 x 3.5 34 mm 1.3386 / 34 36 mm 1.4173 / 36
M33 x 2 34 mm 1.3386 / 34 36 mm 1.4173 / 36
1-3/8-6 1-7/16″ 1.4375 / 36.51 1-1/2″ 1.500 / 38.1
1-3/8-12 1-7/16″ 1.4375 / 36.51 1-1/2″ 1.500 / 38.1
M36 x 4 37 mm 1.4567 / 37 39 mm 1.5354 / 39
M36 x 3 37 mm 1.4567 / 37 39 mm 1.5354 / 39
M36 x 2 37 mm 1.4567 / 37 39 mm 1.5354 / 39
1-1/2-6 1-9/16″ 1.5625 / 39.69 1-5/8″ 1.625 / 41.28
1-1/2-12 1-9/16″ 1.5625 / 39.69 1-5/8″ 1.625 / 41.28
M39 x 4 40 mm 1.5748 / 40 42 mm 1.6535 / 42
M42 x 4.5 43 mm 1.6929 / 43 45 mm 1.7717 / 45
M42 x 3 43 mm 1.6929 / 43 45 mm 1.7717 / 45
M42 x 2 43 mm 1.6929 / 43 45 mm 1.7717 / 45
M45 x 4.5 46 mm 1.811 / 46 48 mm 1.8898 / 48
M48 x 5 50 mm 1.9685 / 50 52 mm 2.0472 / 52
M48 x 3 50 mm 1.9685 / 50 52 mm 2.0472 / 52
M48 x 2 50 mm 1.9685 / 50 52 mm 2.0472 / 52
M52 x 5 54 mm 2.126 / 54 56 mm 2.2047 / 56
M56 x 5.5 58 mm 2.2835 / 58 62 mm 2.4409 / 62
M60 x 5.5 62 mm 2.4409 / 62 66 mm 2.5984 / 66
M64 x 6 66 mm 2.5984 / 66 70 mm 2.7559 / 70

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

Clearance holes are not tapped holes

Worth stating plainly, because it is the commonest mix-up on this site. A tap drill is smaller than the bolt, because the tap has to cut a thread into what is left. A clearance hole is larger than the bolt, because the bolt just passes through. If you drill a clearance hole and then try to tap it, you will get no thread at all.

In a typical bolted joint you want both: a clearance hole in the top part and a tapped hole in the bottom one. Tap drills for all these sizes are on the UNC, UNF and metric charts.

Diameter is all that matters

Clearance is set by the bolt's major diameter, so pitch is irrelevant. Every 1/4 inch thread, coarse or fine or extra fine, takes the same clearance hole; so does every M6. The chart lists each thread on its own row because that is how the question gets asked, but the numbers repeat by design.

Choosing a fit

  • Close / fine. The tightest standard fit. Use it when location matters and you can actually hold the tolerance, for example two machined parts doweled or bored together. It leaves almost no room to adjust.
  • Normal / medium. The default, and the right answer most of the time. It absorbs ordinary machining variation without letting the parts wander.
  • Loose / coarse. For fabricated or welded parts, long bolt patterns where tolerances stack up, and anything assembled on site. Pair it with a washer so the bolt head has something to bear on.

The min and max columns

The inch rows carry a permitted range as well as a drill, because ASME B18.2.8 specifies the finished hole rather than the tool. A drill cuts slightly oversize, especially in a hand drill or a worn chuck, and the range is what the hole is allowed to end up as. Each size's own page shows the full min and max; the chart shows the nominal drill to keep it readable.

Sizes with no published clearance

6 of the threads on this chart fall outside the standards it follows, so their rows show no figure. Those sizes are #12-24 , #12-28 , #12-32 , 9/16-12 , 9/16-18 , 9/16-24 . Each page carries the reason from the data rather than a substitute number; take the hole from your drawing instead.

Frequently asked questions

What is a clearance hole?
The plain, untapped hole the bolt passes through on its way to the tapped part or the nut. It is always larger than the bolt, so the bolt can move sideways enough to line up with the thread on the other side.
What is the clearance hole for a 1/4-20 bolt?
For a normal fit, 9/32″ (0.2812 in), with the finished hole between 0.281 in and 0.290 in per ASME B18.2.8.
What clearance hole does an M6 bolt need?
6.6 mm for a medium fit per ISO 273. Fine and coarse fits are on the chart above.
Does the thread pitch change the clearance hole?
No. Clearance depends on the bolt's major diameter and nothing else, so 1/4-20, 1/4-28 and 1/4-32 all take the same clearance hole. The rows are listed separately here only because that is how people search for them.
Which fit should I use?
Normal (ISO medium) for most work. Close when parts must line up precisely and you can hold position. Loose when there is stack-up to absorb, parts are fabricated rather than machined, or things need to go together on site.
Why do some rows have no clearance hole?
6 sizes are not covered by the standards this chart follows. Those rows say so in the Standard column instead of showing a figure, because a made-up number is worse than no number. Take the hole from your drawing for those.

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