UNEF threads: tap drill size chart
Full chart with the tap drill for every size. Press “Calculate” on any row to open the calculator with that thread.
UNEF is the extra-fine series of the Unified thread: more threads per inch than UNF for the same diameter. It is used on thin walls, fittings, adjusting nuts and in aerospace, where a lot of thread is needed in a short length or a very fine adjustment. 1/4"-32 UNEF has 32 threads per inch, against 28 on UNF and 20 on UNC.
| Thread | Threads per inch | Ø major | Inch drill | Metric drill | Drill for forming tap | Calculate |
|---|---|---|---|---|---|---|
| #12-32 UNEF | 32 | 0.216" · 5.486 mm | #130.185" · 4.7 mm | ⌀ 4.7 | #70.201" · 5.11 mm | |
| 1/4"-32 UNEF | 32 | 0.25" · 6.35 mm | 7/32"0.2188" · 5.56 mm | ⌀ 5.6 | 15/64"0.2344" · 5.95 mm | |
| 5/16"-32 UNEF | 32 | 0.3125" · 7.938 mm | 9/32"0.2813" · 7.14 mm | ⌀ 7.2 | 19/64"0.2969" · 7.54 mm | |
| 3/8"-32 UNEF | 32 | 0.375" · 9.525 mm | 11/32"0.3438" · 8.73 mm | ⌀ 8.8 | 23/64"0.3594" · 9.13 mm | |
| 7/16"-28 UNEF | 28 | 0.4375" · 11.113 mm | Y0.404" · 10.26 mm | ⌀ 10.2 | 27/64"0.4219" · 10.72 mm | |
| 1/2"-28 UNEF | 28 | 0.5" · 12.7 mm | 15/32"0.4688" · 11.91 mm | ⌀ 11.8 | 31/64"0.4844" · 12.3 mm | |
| 9/16"-24 UNEF | 24 | 0.5625" · 14.288 mm | 33/64"0.5156" · 13.1 mm | ⌀ 13.5 | 35/64"0.5469" · 13.89 mm | |
| 5/8"-24 UNEF | 24 | 0.625" · 15.875 mm | 37/64"0.5781" · 14.68 mm | ⌀ 15 | 39/64"0.6094" · 15.48 mm | |
| 3/4"-20 UNEF | 20 | 0.75" · 19.05 mm | 45/64"0.7031" · 17.86 mm | ⌀ 18 | 23/32"0.7188" · 18.26 mm | |
| 7/8"-20 UNEF | 20 | 0.875" · 22.225 mm | 53/64"0.8281" · 21.03 mm | ⌀ 21 | 27/32"0.8438" · 21.43 mm | |
| 1"-20 UNEF | 20 | 1" · 25.4 mm | 61/64"0.9531" · 24.21 mm | ⌀ 24 | 31/32"0.9688" · 24.61 mm | |
| 1-1/16"-18 UNEF | 18 | 1.0625" · 26.988 mm | 1-1/64"1.0156" · 25.8 mm | ⌀ 25.5 | 1-1/32"1.0313" · 26.19 mm | |
| 1-1/8"-18 UNEF | 18 | 1.125" · 28.575 mm | 1-5/64"1.0781" · 27.38 mm | ⌀ 27 | 1-3/32"1.0938" · 27.78 mm | |
| 1-1/4"-18 UNEF | 18 | 1.25" · 31.75 mm | 1-13/64"1.2031" · 30.56 mm | ⌀ 30.5 | 1-7/32"1.2188" · 30.96 mm | |
| 1-5/16"-18 UNEF | 18 | 1.3125" · 33.338 mm | 1-17/64"1.2656" · 32.15 mm | ⌀ 32 | 1-9/32"1.2813" · 32.54 mm | |
| 1-3/8"-18 UNEF | 18 | 1.375" · 34.925 mm | 1-21/64"1.3281" · 33.73 mm | ⌀ 33.5 | 1-11/32"1.3438" · 34.13 mm | |
| 1-1/2"-18 UNEF | 18 | 1.5" · 38.1 mm | 1-29/64"1.4531" · 36.91 mm | ⌀ 36.5 | 1-15/32"1.4688" · 37.31 mm | |
| 1-5/8"-18 UNEF | 18 | 1.625" · 41.275 mm | 1-37/64"1.5781" · 40.08 mm | ⌀ 40 | 1-19/32"1.5938" · 40.48 mm | |
| 1-3/4"-18 UNEF | 18 | 1.75" · 44.45 mm | 1-45/64"1.7031" · 43.26 mm | ⌀ 43 | 1-23/32"1.7188" · 43.66 mm |
How to read the chart
Inch drill: the drill from an inch drill set closest to 75 % thread, the same one the ASME tables give. It can be a number drill (#7), a letter drill (F) or a fraction drill (5/16").
Metric drill: the millimetre drill closest to the same 75 %. It is the one to use when the shop only has metric drills; the difference from the inch drill is a few hundredths.
Forming tap drill: the tap does not cut, it displaces the material, so the hole is larger. Drilling with the cutting-tap drill and tapping with a forming tap breaks it.
"Calculate" opens the calculator with that size: G84 cycle, feed, depth in a blind hole and the recommended method for the material. Guide values for a 2B thread; on critical parts, check against the tap maker's table.
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