---
type: "chart"
name: "Tap drill chart"
thread_count: 184
series_count: 7
default_engagement_pct: 75
tap_type: "cut"
verified: "August 1, 2026"
url: https://shopmath.org/charts/tap-drill
---

# Tap Drill Chart — Every Inch and Metric Thread in One Table

184 threads with their recommended tap drill, in inch and millimetre, at the shop-default thread engagement with a cut tap. Inch and metric sizes are in one table rather than two, because the question "which drill do I grab" does not care which system the thread came from. Each row links to that thread's page, which carries the full 50–85% engagement range, clearance holes and class limits.

## Thread Series in This Chart

| Series | System | Sizes |
| --- | --- | --- |
| [ISO Metric Coarse](https://shopmath.org/threads/metric-coarse.md) | metric | 31 |
| [ISO Metric Fine](https://shopmath.org/threads/metric-fine.md) | metric | 37 |
| [NPT Taper Pipe Thread](https://shopmath.org/threads/npt.md) | pipe | 24 |
| [NPTF Dryseal Pipe Thread](https://shopmath.org/threads/nptf.md) | pipe | 10 |
| [Unified Coarse (UNC)](https://shopmath.org/threads/unc.md) | unified | 33 |
| [Unified Extra Fine (UNEF)](https://shopmath.org/threads/unef.md) | unified | 25 |
| [Unified Fine (UNF)](https://shopmath.org/threads/unf.md) | unified | 24 |

## Tap Drill Sizes for Every Thread

Ordered by system, then series, then size. Thread % is what the listed drill actually leaves, not the requested target.

| Thread | Series | TPI / pitch | Tap drill | Drill Ø (in) | Drill Ø (mm) | Thread % |
| --- | --- | --- | --- | --- | --- | --- |
| [M1.6×0.35](https://shopmath.org/threads/metric-coarse/m1.6x0.35.md) | Metric coarse | 0.350 mm | 1.25 mm | 0.0492 | 1.250 | 77.0 |
| [M1.8×0.35](https://shopmath.org/threads/metric-coarse/m1.8x0.35.md) | Metric coarse | 0.350 mm | 1.45 mm | 0.0571 | 1.450 | 77.0 |
| [M2×0.4](https://shopmath.org/threads/metric-coarse/m2x0.4.md) | Metric coarse | 0.400 mm | 1.6 mm | 0.0630 | 1.600 | 77.0 |
| [M2.5×0.45](https://shopmath.org/threads/metric-coarse/m2.5x0.45.md) | Metric coarse | 0.450 mm | 2.05 mm | 0.0807 | 2.050 | 77.0 |
| [M3×0.5](https://shopmath.org/threads/metric-coarse/m3x0.5.md) | Metric coarse | 0.500 mm | 2.5 mm | 0.0984 | 2.500 | 77.0 |
| [M3.5×0.6](https://shopmath.org/threads/metric-coarse/m3.5x0.6.md) | Metric coarse | 0.600 mm | 2.9 mm | 0.1142 | 2.900 | 77.0 |
| [M4×0.7](https://shopmath.org/threads/metric-coarse/m4x0.7.md) | Metric coarse | 0.700 mm | 3.3 mm | 0.1299 | 3.300 | 77.0 |
| [M5×0.8](https://shopmath.org/threads/metric-coarse/m5x0.8.md) | Metric coarse | 0.800 mm | 4.2 mm | 0.1653 | 4.200 | 77.0 |
| [M6×1](https://shopmath.org/threads/metric-coarse/m6x1.md) | Metric coarse | 1.000 mm | 5 mm | 0.1968 | 5.000 | 77.0 |
| [M7×1](https://shopmath.org/threads/metric-coarse/m7x1.md) | Metric coarse | 1.000 mm | 6 mm | 0.2362 | 6.000 | 77.0 |
| [M8×1.25](https://shopmath.org/threads/metric-coarse/m8x1.25.md) | Metric coarse | 1.250 mm | 6.8 mm | 0.2677 | 6.800 | 73.9 |
| [M10×1.5](https://shopmath.org/threads/metric-coarse/m10x1.5.md) | Metric coarse | 1.500 mm | 8.5 mm | 0.3347 | 8.500 | 77.0 |
| [M12×1.75](https://shopmath.org/threads/metric-coarse/m12x1.75.md) | Metric coarse | 1.750 mm | 10.3 mm | 0.4055 | 10.300 | 74.8 |
| [M14×2](https://shopmath.org/threads/metric-coarse/m14x2.md) | Metric coarse | 2.000 mm | 12.1 mm | 0.4764 | 12.100 | 73.1 |
| [M16×2](https://shopmath.org/threads/metric-coarse/m16x2.md) | Metric coarse | 2.000 mm | 14 mm | 0.5512 | 14.000 | 77.0 |
| [M18×2.5](https://shopmath.org/threads/metric-coarse/m18x2.5.md) | Metric coarse | 2.500 mm | 15.5 mm | 0.6102 | 15.500 | 77.0 |
| [M20×2.5](https://shopmath.org/threads/metric-coarse/m20x2.5.md) | Metric coarse | 2.500 mm | 17.5 mm | 0.6890 | 17.500 | 77.0 |
| [M22×2.5](https://shopmath.org/threads/metric-coarse/m22x2.5.md) | Metric coarse | 2.500 mm | 19.5 mm | 0.7677 | 19.500 | 77.0 |
| [M24×3](https://shopmath.org/threads/metric-coarse/m24x3.md) | Metric coarse | 3.000 mm | 21 mm | 0.8268 | 21.000 | 77.0 |
| [M27×3](https://shopmath.org/threads/metric-coarse/m27x3.md) | Metric coarse | 3.000 mm | 24 mm | 0.9449 | 24.000 | 77.0 |
| [M30×3.5](https://shopmath.org/threads/metric-coarse/m30x3.5.md) | Metric coarse | 3.500 mm | 25 mm | 0.9842 | 25.000 | 110.0 |
| [M33×3.5](https://shopmath.org/threads/metric-coarse/m33x3.5.md) | Metric coarse | 3.500 mm | 25 mm | 0.9842 | 25.000 | 176.0 |
| [M36×4](https://shopmath.org/threads/metric-coarse/m36x4.md) | Metric coarse | 4.000 mm | 25 mm | 0.9842 | 25.000 | 211.7 |
| [M39×4](https://shopmath.org/threads/metric-coarse/m39x4.md) | Metric coarse | 4.000 mm | 25 mm | 0.9842 | 25.000 | 269.4 |
| [M42×4.5](https://shopmath.org/threads/metric-coarse/m42x4.5.md) | Metric coarse | 4.500 mm | 25 mm | 0.9842 | 25.000 | 290.8 |
| [M45×4.5](https://shopmath.org/threads/metric-coarse/m45x4.5.md) | Metric coarse | 4.500 mm | 25 mm | 0.9842 | 25.000 | 342.1 |
| [M48×5](https://shopmath.org/threads/metric-coarse/m48x5.md) | Metric coarse | 5.000 mm | 25 mm | 0.9842 | 25.000 | 354.1 |
| [M52×5](https://shopmath.org/threads/metric-coarse/m52x5.md) | Metric coarse | 5.000 mm | 25 mm | 0.9842 | 25.000 | 415.7 |
| [M56×5.5](https://shopmath.org/threads/metric-coarse/m56x5.5.md) | Metric coarse | 5.500 mm | 25 mm | 0.9842 | 25.000 | 433.9 |
| [M60×5.5](https://shopmath.org/threads/metric-coarse/m60x5.5.md) | Metric coarse | 5.500 mm | 25 mm | 0.9842 | 25.000 | 489.9 |
| [M64×6](https://shopmath.org/threads/metric-coarse/m64x6.md) | Metric coarse | 6.000 mm | 25 mm | 0.9842 | 25.000 | 500.4 |
| [M1.6×0.2](https://shopmath.org/threads/metric-fine/m1.6x0.2.md) | Metric fine | 0.200 mm | 1.4 mm | 0.0551 | 1.400 | 77.0 |
| [M1.8×0.2](https://shopmath.org/threads/metric-fine/m1.8x0.2.md) | Metric fine | 0.200 mm | 1.6 mm | 0.0630 | 1.600 | 77.0 |
| [M2×0.25](https://shopmath.org/threads/metric-fine/m2x0.25.md) | Metric fine | 0.250 mm | 1.75 mm | 0.0689 | 1.750 | 77.0 |
| [M2.5×0.35](https://shopmath.org/threads/metric-fine/m2.5x0.35.md) | Metric fine | 0.350 mm | 2.15 mm | 0.0847 | 2.150 | 77.0 |
| [M3×0.35](https://shopmath.org/threads/metric-fine/m3x0.35.md) | Metric fine | 0.350 mm | 2.65 mm | 0.1043 | 2.650 | 77.0 |
| [M3.5×0.35](https://shopmath.org/threads/metric-fine/m3.5x0.35.md) | Metric fine | 0.350 mm | 3.2 mm | 0.1260 | 3.200 | 66.0 |
| [M4×0.5](https://shopmath.org/threads/metric-fine/m4x0.5.md) | Metric fine | 0.500 mm | 3.5 mm | 0.1378 | 3.500 | 77.0 |
| [M5×0.5](https://shopmath.org/threads/metric-fine/m5x0.5.md) | Metric fine | 0.500 mm | 4.5 mm | 0.1772 | 4.500 | 77.0 |
| [M6×0.75](https://shopmath.org/threads/metric-fine/m6x0.75.md) | Metric fine | 0.750 mm | 5.3 mm | 0.2087 | 5.300 | 71.8 |
| [M7×0.75](https://shopmath.org/threads/metric-fine/m7x0.75.md) | Metric fine | 0.750 mm | 6.3 mm | 0.2480 | 6.300 | 71.8 |
| [M8×0.75](https://shopmath.org/threads/metric-fine/m8x0.75.md) | Metric fine | 0.750 mm | 7.3 mm | 0.2874 | 7.300 | 71.8 |
| [M8×1](https://shopmath.org/threads/metric-fine/m8x1.md) | Metric fine | 1.000 mm | 7 mm | 0.2756 | 7.000 | 77.0 |
| [M10×1](https://shopmath.org/threads/metric-fine/m10x1.md) | Metric fine | 1.000 mm | 9 mm | 0.3543 | 9.000 | 77.0 |
| [M10×1.25](https://shopmath.org/threads/metric-fine/m10x1.25.md) | Metric fine | 1.250 mm | 8.8 mm | 0.3465 | 8.800 | 73.9 |
| [M12×1.25](https://shopmath.org/threads/metric-fine/m12x1.25.md) | Metric fine | 1.250 mm | 10.8 mm | 0.4252 | 10.800 | 73.9 |
| [M12×1.5](https://shopmath.org/threads/metric-fine/m12x1.5.md) | Metric fine | 1.500 mm | 10.5 mm | 0.4134 | 10.500 | 77.0 |
| [M14×1.5](https://shopmath.org/threads/metric-fine/m14x1.5.md) | Metric fine | 1.500 mm | 12.5 mm | 0.4921 | 12.500 | 77.0 |
| [M16×1.5](https://shopmath.org/threads/metric-fine/m16x1.5.md) | Metric fine | 1.500 mm | 14.5 mm | 0.5709 | 14.500 | 77.0 |
| [M18×1.5](https://shopmath.org/threads/metric-fine/m18x1.5.md) | Metric fine | 1.500 mm | 16.5 mm | 0.6496 | 16.500 | 77.0 |
| [M18×2](https://shopmath.org/threads/metric-fine/m18x2.md) | Metric fine | 2.000 mm | 16 mm | 0.6299 | 16.000 | 77.0 |
| [M20×1.5](https://shopmath.org/threads/metric-fine/m20x1.5.md) | Metric fine | 1.500 mm | 18.5 mm | 0.7284 | 18.500 | 77.0 |
| [M20×2](https://shopmath.org/threads/metric-fine/m20x2.md) | Metric fine | 2.000 mm | 18 mm | 0.7087 | 18.000 | 77.0 |
| [M22×1.5](https://shopmath.org/threads/metric-fine/m22x1.5.md) | Metric fine | 1.500 mm | 20.5 mm | 0.8071 | 20.500 | 77.0 |
| [M22×2](https://shopmath.org/threads/metric-fine/m22x2.md) | Metric fine | 2.000 mm | 20 mm | 0.7874 | 20.000 | 77.0 |
| [M24×2](https://shopmath.org/threads/metric-fine/m24x2.md) | Metric fine | 2.000 mm | 22 mm | 0.8661 | 22.000 | 77.0 |
| [M27×2](https://shopmath.org/threads/metric-fine/m27x2.md) | Metric fine | 2.000 mm | 25 mm | 0.9842 | 25.000 | 77.0 |
| [M30×2](https://shopmath.org/threads/metric-fine/m30x2.md) | Metric fine | 2.000 mm | 25 mm | 0.9842 | 25.000 | 192.4 |
| [M33×2](https://shopmath.org/threads/metric-fine/m33x2.md) | Metric fine | 2.000 mm | 25 mm | 0.9842 | 25.000 | 307.9 |
| [M36×3](https://shopmath.org/threads/metric-fine/m36x3.md) | Metric fine | 3.000 mm | 25 mm | 0.9842 | 25.000 | 282.3 |
| [M39×3](https://shopmath.org/threads/metric-fine/m39x3.md) | Metric fine | 3.000 mm | 25 mm | 0.9842 | 25.000 | 359.2 |
| [M42×3](https://shopmath.org/threads/metric-fine/m42x3.md) | Metric fine | 3.000 mm | 25 mm | 0.9842 | 25.000 | 436.2 |
| [M45×3](https://shopmath.org/threads/metric-fine/m45x3.md) | Metric fine | 3.000 mm | 25 mm | 0.9842 | 25.000 | 513.2 |
| [M48×3](https://shopmath.org/threads/metric-fine/m48x3.md) | Metric fine | 3.000 mm | 25 mm | 0.9842 | 25.000 | 590.2 |
| [M52×4](https://shopmath.org/threads/metric-fine/m52x4.md) | Metric fine | 4.000 mm | 25 mm | 0.9842 | 25.000 | 519.6 |
| [M56×4](https://shopmath.org/threads/metric-fine/m56x4.md) | Metric fine | 4.000 mm | 25 mm | 0.9842 | 25.000 | 596.6 |
| [M60×4](https://shopmath.org/threads/metric-fine/m60x4.md) | Metric fine | 4.000 mm | 25 mm | 0.9842 | 25.000 | 673.6 |
| [M64×4](https://shopmath.org/threads/metric-fine/m64x4.md) | Metric fine | 4.000 mm | 25 mm | 0.9842 | 25.000 | 750.6 |
| [1/16-27 NPT](https://shopmath.org/threads/npt/1-16.md) | NPT | 27 | E | 0.2500 | 6.350 | — |
| [1/8-27 NPT](https://shopmath.org/threads/npt/1-8.md) | NPT | 27 | 11/32 | 0.3438 | 8.731 | — |
| [1/4-18 NPT](https://shopmath.org/threads/npt/1-4.md) | NPT | 18 | 7/16 | 0.4375 | 11.113 | — |
| [3/8-18 NPT](https://shopmath.org/threads/npt/3-8.md) | NPT | 18 | 37/64 | 0.5781 | 14.684 | — |
| [1/2-14 NPT](https://shopmath.org/threads/npt/1-2.md) | NPT | 14 | 23/32 | 0.7188 | 18.256 | — |
| [3/4-14 NPT](https://shopmath.org/threads/npt/3-4.md) | NPT | 14 | 59/64 | 0.9219 | 23.416 | — |
| [1-11.5 NPT](https://shopmath.org/threads/npt/1.md) | NPT | 12 | 1 | 1.0000 | 25.400 | — |
| [1 1/4-11.5 NPT](https://shopmath.org/threads/npt/1-1-4.md) | NPT | 12 | 1 | 1.0000 | 25.400 | — |
| [1 1/2-11.5 NPT](https://shopmath.org/threads/npt/1-1-2.md) | NPT | 12 | 1 | 1.0000 | 25.400 | — |
| [2-11.5 NPT](https://shopmath.org/threads/npt/2.md) | NPT | 12 | 1 | 1.0000 | 25.400 | — |
| [2 1/2-8 NPT](https://shopmath.org/threads/npt/2-1-2.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [3-8 NPT](https://shopmath.org/threads/npt/3.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [3 1/2-8 NPT](https://shopmath.org/threads/npt/3-1-2.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [4-8 NPT](https://shopmath.org/threads/npt/4.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [5-8 NPT](https://shopmath.org/threads/npt/5.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [6-8 NPT](https://shopmath.org/threads/npt/6.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [8-8 NPT](https://shopmath.org/threads/npt/8.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [10-8 NPT](https://shopmath.org/threads/npt/10.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [12-8 NPT](https://shopmath.org/threads/npt/12.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [14-8 NPT](https://shopmath.org/threads/npt/14.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [16-8 NPT](https://shopmath.org/threads/npt/16.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [18-8 NPT](https://shopmath.org/threads/npt/18.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [20-8 NPT](https://shopmath.org/threads/npt/20.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [24-8 NPT](https://shopmath.org/threads/npt/24.md) | NPT | 8 | 1 | 1.0000 | 25.400 | — |
| [1/16-27 NPTF](https://shopmath.org/threads/nptf/1-16.md) | NPTF | 27 | E | 0.2500 | 6.350 | — |
| [1/8-27 NPTF](https://shopmath.org/threads/nptf/1-8.md) | NPTF | 27 | 11/32 | 0.3438 | 8.731 | — |
| [1/4-18 NPTF](https://shopmath.org/threads/nptf/1-4.md) | NPTF | 18 | 7/16 | 0.4375 | 11.113 | — |
| [3/8-18 NPTF](https://shopmath.org/threads/nptf/3-8.md) | NPTF | 18 | 37/64 | 0.5781 | 14.684 | — |
| [1/2-14 NPTF](https://shopmath.org/threads/nptf/1-2.md) | NPTF | 14 | 23/32 | 0.7188 | 18.256 | — |
| [3/4-14 NPTF](https://shopmath.org/threads/nptf/3-4.md) | NPTF | 14 | 59/64 | 0.9219 | 23.416 | — |
| [1-11.5 NPTF](https://shopmath.org/threads/nptf/1.md) | NPTF | 12 | 1 | 1.0000 | 25.400 | — |
| [1 1/4-11.5 NPTF](https://shopmath.org/threads/nptf/1-1-4.md) | NPTF | 12 | 1 | 1.0000 | 25.400 | — |
| [1 1/2-11.5 NPTF](https://shopmath.org/threads/nptf/1-1-2.md) | NPTF | 12 | 1 | 1.0000 | 25.400 | — |
| [2-11.5 NPTF](https://shopmath.org/threads/nptf/2.md) | NPTF | 12 | 1 | 1.0000 | 25.400 | — |
| [#1-64 UNC](https://shopmath.org/threads/unc/1-64.md) | UNC | 64 | #53 | 0.0595 | 1.511 | 66.5 |
| [#2-56 UNC](https://shopmath.org/threads/unc/2-56.md) | UNC | 56 | #50 | 0.0700 | 1.778 | 69.0 |
| [#3-48 UNC](https://shopmath.org/threads/unc/3-48.md) | UNC | 48 | #47 | 0.0785 | 1.994 | 75.7 |
| [#4-40 UNC](https://shopmath.org/threads/unc/4-40.md) | UNC | 40 | #43 | 0.0890 | 2.261 | 70.8 |
| [#5-40 UNC](https://shopmath.org/threads/unc/5-40.md) | UNC | 40 | #38 | 0.1015 | 2.578 | 72.4 |
| [#6-32 UNC](https://shopmath.org/threads/unc/6-32.md) | UNC | 32 | #36 | 0.1065 | 2.705 | 77.6 |
| [#8-32 UNC](https://shopmath.org/threads/unc/8-32.md) | UNC | 32 | #29 | 0.1360 | 3.454 | 69.0 |
| [#10-24 UNC](https://shopmath.org/threads/unc/10-24.md) | UNC | 24 | #25 | 0.1495 | 3.797 | 74.8 |
| [#12-24 UNC](https://shopmath.org/threads/unc/12-24.md) | UNC | 24 | #16 | 0.1770 | 4.496 | 72.1 |
| [1/4"-20 UNC](https://shopmath.org/threads/unc/1-4-20.md) | UNC | 20 | #7 | 0.2010 | 5.105 | 75.4 |
| [5/16"-18 UNC](https://shopmath.org/threads/unc/5-16-18.md) | UNC | 18 | F | 0.2570 | 6.528 | 76.9 |
| [3/8"-16 UNC](https://shopmath.org/threads/unc/3-8-16.md) | UNC | 16 | 5/16 | 0.3125 | 7.938 | 77.0 |
| [7/16"-14 UNC](https://shopmath.org/threads/unc/7-16-14.md) | UNC | 14 | U | 0.3680 | 9.347 | 74.9 |
| [1/2"-13 UNC](https://shopmath.org/threads/unc/1-2-13.md) | UNC | 13 | 27/64 | 0.4219 | 10.716 | 78.2 |
| [9/16"-12 UNC](https://shopmath.org/threads/unc/9-16-12.md) | UNC | 12 | 31/64 | 0.4844 | 12.303 | 72.2 |
| [5/8"-11 UNC](https://shopmath.org/threads/unc/5-8-11.md) | UNC | 11 | 17/32 | 0.5313 | 13.494 | 79.4 |
| [3/4"-10 UNC](https://shopmath.org/threads/unc/3-4-10.md) | UNC | 10 | 21/32 | 0.6563 | 16.669 | 72.2 |
| [7/8"-9 UNC](https://shopmath.org/threads/unc/7-8-9.md) | UNC | 9 | 49/64 | 0.7656 | 19.447 | 75.8 |
| [1"-8 UNC](https://shopmath.org/threads/unc/1-8.md) | UNC | 8 | 7/8 | 0.8750 | 22.225 | 77.0 |
| [1 1/8"-7 UNC](https://shopmath.org/threads/unc/1-1-8-7.md) | UNC | 7 | 63/64 | 0.9844 | 25.003 | 75.8 |
| [1 1/4"-7 UNC](https://shopmath.org/threads/unc/1-1-4-7.md) | UNC | 7 | 1 | 1.0000 | 25.400 | 134.7 |
| [1 3/8"-6 UNC](https://shopmath.org/threads/unc/1-3-8-6.md) | UNC | 6 | 1 | 1.0000 | 25.400 | 173.2 |
| [1 1/2"-6 UNC](https://shopmath.org/threads/unc/1-1-2-6.md) | UNC | 6 | 1 | 1.0000 | 25.400 | 230.9 |
| [1 3/4"-5 UNC](https://shopmath.org/threads/unc/1-3-4-5.md) | UNC | 5 | 1 | 1.0000 | 25.400 | 288.7 |
| [2"-4 UNC](https://shopmath.org/threads/unc/2-4.md) | UNC | 4 | 1 | 1.0000 | 25.400 | 307.9 |
| [2 1/4"-4 UNC](https://shopmath.org/threads/unc/2-1-4-4.md) | UNC | 4 | 1 | 1.0000 | 25.400 | 384.9 |
| [2 1/2"-4 UNC](https://shopmath.org/threads/unc/2-1-2-4.md) | UNC | 4 | 1 | 1.0000 | 25.400 | 461.9 |
| [2 3/4"-4 UNC](https://shopmath.org/threads/unc/2-3-4-4.md) | UNC | 4 | 1 | 1.0000 | 25.400 | 538.9 |
| [3"-4 UNC](https://shopmath.org/threads/unc/3-4.md) | UNC | 4 | 1 | 1.0000 | 25.400 | 615.8 |
| [3 1/4"-4 UNC](https://shopmath.org/threads/unc/3-1-4-4.md) | UNC | 4 | 1 | 1.0000 | 25.400 | 692.8 |
| [3 1/2"-4 UNC](https://shopmath.org/threads/unc/3-1-2-4.md) | UNC | 4 | 1 | 1.0000 | 25.400 | 769.8 |
| [3 3/4"-4 UNC](https://shopmath.org/threads/unc/3-3-4-4.md) | UNC | 4 | 1 | 1.0000 | 25.400 | 846.8 |
| [4"-4 UNC](https://shopmath.org/threads/unc/4-4.md) | UNC | 4 | 1 | 1.0000 | 25.400 | 923.8 |
| [#12-32 UNEF](https://shopmath.org/threads/unef/12-32.md) | UNEF | 32 | #13 | 0.1850 | 4.699 | 76.4 |
| [1/4"-32 UNEF](https://shopmath.org/threads/unef/1-4-32.md) | UNEF | 32 | 7/32 | 0.2188 | 5.556 | 77.0 |
| [5/16"-32 UNEF](https://shopmath.org/threads/unef/5-16-32.md) | UNEF | 32 | 9/32 | 0.2813 | 7.144 | 77.0 |
| [3/8"-32 UNEF](https://shopmath.org/threads/unef/3-8-32.md) | UNEF | 32 | 11/32 | 0.3438 | 8.731 | 77.0 |
| [7/16"-28 UNEF](https://shopmath.org/threads/unef/7-16-28.md) | UNEF | 28 | Y | 0.4040 | 10.262 | 72.2 |
| [1/2"-28 UNEF](https://shopmath.org/threads/unef/1-2-28.md) | UNEF | 28 | 15/32 | 0.4688 | 11.906 | 67.4 |
| [9/16"-24 UNEF](https://shopmath.org/threads/unef/9-16-24.md) | UNEF | 24 | 33/64 | 0.5156 | 13.097 | 86.6 |
| [5/8"-24 UNEF](https://shopmath.org/threads/unef/5-8-24.md) | UNEF | 24 | 37/64 | 0.5781 | 14.684 | 86.6 |
| [11/16"-24 UNEF](https://shopmath.org/threads/unef/11-16-24.md) | UNEF | 24 | 41/64 | 0.6406 | 16.272 | 86.6 |
| [3/4"-20 UNEF](https://shopmath.org/threads/unef/3-4-20.md) | UNEF | 20 | 45/64 | 0.7031 | 17.859 | 72.2 |
| [13/16"-20 UNEF](https://shopmath.org/threads/unef/13-16-20.md) | UNEF | 20 | 49/64 | 0.7656 | 19.447 | 72.2 |
| [7/8"-20 UNEF](https://shopmath.org/threads/unef/7-8-20.md) | UNEF | 20 | 53/64 | 0.8281 | 21.034 | 72.2 |
| [15/16"-20 UNEF](https://shopmath.org/threads/unef/15-16-20.md) | UNEF | 20 | 57/64 | 0.8906 | 22.622 | 72.2 |
| [1"-20 UNEF](https://shopmath.org/threads/unef/1-20.md) | UNEF | 20 | 61/64 | 0.9531 | 24.209 | 72.2 |
| [1 1/16"-18 UNEF](https://shopmath.org/threads/unef/1-1-16-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 86.6 |
| [1 1/8"-18 UNEF](https://shopmath.org/threads/unef/1-1-8-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 173.2 |
| [1 3/16"-18 UNEF](https://shopmath.org/threads/unef/1-3-16-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 259.8 |
| [1 1/4"-18 UNEF](https://shopmath.org/threads/unef/1-1-4-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 346.4 |
| [1 5/16"-18 UNEF](https://shopmath.org/threads/unef/1-5-16-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 433.0 |
| [1 3/8"-18 UNEF](https://shopmath.org/threads/unef/1-3-8-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 519.6 |
| [1 7/16"-18 UNEF](https://shopmath.org/threads/unef/1-7-16-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 606.2 |
| [1 1/2"-18 UNEF](https://shopmath.org/threads/unef/1-1-2-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 692.8 |
| [1 9/16"-18 UNEF](https://shopmath.org/threads/unef/1-9-16-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 779.4 |
| [1 5/8"-18 UNEF](https://shopmath.org/threads/unef/1-5-8-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 866.0 |
| [1 11/16"-18 UNEF](https://shopmath.org/threads/unef/1-11-16-18.md) | UNEF | 18 | 1 | 1.0000 | 25.400 | 952.6 |
| [#0-80 UNF](https://shopmath.org/threads/unf/0-80.md) | UNF | 80 | 3/64 | 0.0469 | 1.191 | 80.8 |
| [#1-72 UNF](https://shopmath.org/threads/unf/1-72.md) | UNF | 72 | #53 | 0.0595 | 1.511 | 74.8 |
| [#2-64 UNF](https://shopmath.org/threads/unf/2-64.md) | UNF | 64 | #50 | 0.0700 | 1.778 | 78.8 |
| [#3-56 UNF](https://shopmath.org/threads/unf/3-56.md) | UNF | 56 | #45 | 0.0820 | 2.083 | 73.3 |
| [#4-48 UNF](https://shopmath.org/threads/unf/4-48.md) | UNF | 48 | #42 | 0.0935 | 2.375 | 68.4 |
| [#5-44 UNF](https://shopmath.org/threads/unf/5-44.md) | UNF | 44 | #37 | 0.1040 | 2.642 | 71.1 |
| [#6-40 UNF](https://shopmath.org/threads/unf/6-40.md) | UNF | 40 | #33 | 0.1130 | 2.870 | 77.0 |
| [#8-36 UNF](https://shopmath.org/threads/unf/8-36.md) | UNF | 36 | #29 | 0.1360 | 3.454 | 77.6 |
| [#10-32 UNF](https://shopmath.org/threads/unf/10-32.md) | UNF | 32 | #21 | 0.1590 | 4.039 | 76.4 |
| [#12-28 UNF](https://shopmath.org/threads/unf/12-28.md) | UNF | 28 | #14 | 0.1820 | 4.623 | 73.3 |
| [1/4"-28 UNF](https://shopmath.org/threads/unf/1-4-28.md) | UNF | 28 | #3 | 0.2130 | 5.410 | 79.8 |
| [5/16"-24 UNF](https://shopmath.org/threads/unf/5-16-24.md) | UNF | 24 | I | 0.2720 | 6.909 | 74.8 |
| [3/8"-24 UNF](https://shopmath.org/threads/unf/3-8-24.md) | UNF | 24 | Q | 0.3320 | 8.433 | 79.4 |
| [7/16"-20 UNF](https://shopmath.org/threads/unf/7-16-20.md) | UNF | 20 | 25/64 | 0.3906 | 9.922 | 72.2 |
| [1/2"-20 UNF](https://shopmath.org/threads/unf/1-2-20.md) | UNF | 20 | 29/64 | 0.4531 | 11.509 | 72.2 |
| [9/16"-18 UNF](https://shopmath.org/threads/unf/9-16-18.md) | UNF | 18 | 33/64 | 0.5156 | 13.097 | 65.0 |
| [5/8"-18 UNF](https://shopmath.org/threads/unf/5-8-18.md) | UNF | 18 | 37/64 | 0.5781 | 14.684 | 65.0 |
| [3/4"-16 UNF](https://shopmath.org/threads/unf/3-4-16.md) | UNF | 16 | 11/16 | 0.6875 | 17.462 | 77.0 |
| [7/8"-14 UNF](https://shopmath.org/threads/unf/7-8-14.md) | UNF | 14 | 13/16 | 0.8125 | 20.637 | 67.4 |
| [1"-12 UNF](https://shopmath.org/threads/unf/1-12.md) | UNF | 12 | 59/64 | 0.9219 | 23.416 | 72.2 |
| [1 1/8"-12 UNF](https://shopmath.org/threads/unf/1-1-8-12.md) | UNF | 12 | 1 | 1.0000 | 25.400 | 115.5 |
| [1 1/4"-12 UNF](https://shopmath.org/threads/unf/1-1-4-12.md) | UNF | 12 | 1 | 1.0000 | 25.400 | 230.9 |
| [1 3/8"-12 UNF](https://shopmath.org/threads/unf/1-3-8-12.md) | UNF | 12 | 1 | 1.0000 | 25.400 | 346.4 |
| [1 1/2"-12 UNF](https://shopmath.org/threads/unf/1-1-2-12.md) | UNF | 12 | 1 | 1.0000 | 25.400 | 461.9 |

_Values are for cut taps. Form (roll) taps need a larger hole and are outside this dataset._

## Where This Chart Differs From the Traditional One

4 threads where the computed nearest-standard-drill recommendation and the traditionally published chart disagree. Both numbers are shown so the difference is a decision, not a surprise.

| Thread | Computed | Traditional chart | Why they differ |
| --- | --- | --- | --- |
| [#12-32 UNEF](https://shopmath.org/threads/unef/12-32.md) | #13 | 3/16 | Computed 75% target 0.1856 in. Nearest standard drill is #13 (0.185 in, off by 0.0006 in); the traditional published chart lists 3/16 (0.188 in, off by 0.0024 in, 69% thread). Both are shown; neither overrides the other. |
| [9/16-18 UNF](https://shopmath.org/threads/unf/9-16-18.md) | 33/64 | 1/2 | Computed 75% target 0.5084 in. Nearest standard drill is 33/64 (0.515625 in, off by 0.0073 in); the traditional published chart lists 1/2 (0.5 in, off by 0.0084 in, 86.6% thread). Both are shown; neither overrides the other. |
| [5/8-18 UNF](https://shopmath.org/threads/unf/5-8-18.md) | 37/64 | 9/16 | Computed 75% target 0.5709 in. Nearest standard drill is 37/64 (0.578125 in, off by 0.0073 in); the traditional published chart lists 9/16 (0.563 in, off by 0.0079 in, 85.9% thread). Both are shown; neither overrides the other. |
| [7/8-14 UNF](https://shopmath.org/threads/unf/7-8-14.md) | 13/16 | 51/64 | Computed 75% target 0.8054 in. Nearest standard drill is 13/16 (0.8125 in, off by 0.0071 in); the traditional published chart lists 51/64 (0.797 in, off by 0.0084 in, 84.1% thread). Both are shown; neither overrides the other. |

## Sources and Method for the Tap Drill Chart

### ISO metric screw threads — M1.6 to M64, coarse and fine

- **Source**: ISO 68-1 basic profile computed; ISO 261/262 diameter-pitch pairs and 6H class limits compiled
- **Method**: computed+compiled
- **Verified against**: threads-metric: 215 checks passed across 3 harness(es)

### NPT and NPTF taper pipe threads

- **Source**: ASME B1.20.1 taper formulas computed; pipe OD, tpi, L1 and L4 compiled
- **Method**: computed+compiled
- **Verified against**: threads-pipe: 98 checks passed across 1 harness(es)

### Unified inch screw threads — UNC, UNF, UNEF

- **Source**: NBS Handbook H28 (1969) Part I §§6-7 formula system (public domain, 17 U.S.C. 105)
- **Method**: computed
- **Verified against**: threads-unified: 1064 checks passed across 3 harness(es)

### Formulas

**Tap drill hole diameter**

```text
inch:    hole Ø  =  D − (%thread ÷ 100) × (1.29904 ÷ n)
metric:  hole Ø  =  D − (%thread ÷ 100) × 1.29904 × P
```

_1.29904 = 2 × 0.64952, twice the engaged thread height per side on the 60° profile._

### Assumptions

- The chart figure assumes the shop-default thread engagement with a cut tap. Every thread page carries 50–85%.
- Drill diameters are nominal; a worn or run-out drill cuts oversize and reduces engagement further.
- ISO metric screw threads — M1.6 to M64, coarse and fine — EXCLUDED: ISO 965-1 tolerance-grade formulas (not located — data-sourcing.md open item 2), 6g external limits (single-sourced), form tap drills, M68-M100 (verified demand cliff at M64).
- NPT and NPTF taper pipe threads — L1 is tabulated, not derivable (data-sourcing.md §3.3). EXCLUDED: NPTF crest/root truncation limits (single-sourced), NPSM/NPSC/NPSF straight pipe threads, BSPT/BSPP.
- Unified inch screw threads — UNC, UNF, UNEF — Le = 1D for UNC/UNF, 9P for UNEF — determined empirically against H28 Table 2.21, resolving data-sourcing.md open item 5. EXCLUDED: form (roll) tap drills, class 1A/1B limits, class 1AR allowances, constant-pitch UN series.

**Data last verified**: August 1, 2026

## Related pages

- Thread series: [Screw thread reference](https://shopmath.org/threads.md)
- Drill sizes: [Drill bit size reference](https://shopmath.org/drills.md)
- Complete drill index: [Drill size chart](https://shopmath.org/charts/drill-sizes.md)

---

*Source: [ShopMath](https://shopmath.org/charts/tap-drill) — data verified August 1, 2026. Reference data; verify against the governing standard before manufacture.*