UNC 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.
UNC is the Unified coarse thread: the default thread on inch fasteners. The diameter is given as a fraction of an inch (or as a number, #1 to #12, below 1/4") and the pitch in threads per inch: 1/4"-20 UNC has 20 threads in every inch. In Spain it turns up mostly on machinery, hydraulics and spare parts of US origin.
| Thread | Threads per inch | Ø major | Inch drill | Metric drill | Drill for forming tap | Calculate |
|---|---|---|---|---|---|---|
| #1-64 UNC | 64 | 0.073" · 1.854 mm | #530.0595" · 1.51 mm | ⌀ 1.45 | #520.0635" · 1.61 mm | |
| #2-56 UNC | 56 | 0.086" · 2.184 mm | #500.07" · 1.78 mm | ⌀ 1.75 | #480.076" · 1.93 mm | |
| #3-48 UNC | 48 | 0.099" · 2.515 mm | #470.0785" · 1.99 mm | ⌀ 2 | #430.089" · 2.26 mm | |
| #4-40 UNC | 40 | 0.112" · 2.845 mm | #430.089" · 2.26 mm | ⌀ 2.25 | #390.0995" · 2.53 mm | |
| #5-40 UNC | 40 | 0.125" · 3.175 mm | #380.1015" · 2.58 mm | ⌀ 2.55 | #330.113" · 2.87 mm | |
| #6-32 UNC | 32 | 0.138" · 3.505 mm | #360.1065" · 2.71 mm | ⌀ 2.75 | #310.12" · 3.05 mm | |
| #8-32 UNC | 32 | 0.164" · 4.166 mm | #290.136" · 3.45 mm | ⌀ 3.4 | #250.1495" · 3.8 mm | |
| #10-24 UNC | 24 | 0.19" · 4.826 mm | #250.1495" · 3.8 mm | ⌀ 3.8 | #180.1695" · 4.31 mm | |
| #12-24 UNC | 24 | 0.216" · 5.486 mm | #160.177" · 4.5 mm | ⌀ 4.5 | #90.196" · 4.98 mm | |
| 1/4"-20 UNC | 20 | 0.25" · 6.35 mm | #70.201" · 5.11 mm | ⌀ 5.1 | #10.228" · 5.79 mm | |
| 5/16"-18 UNC | 18 | 0.3125" · 7.938 mm | F0.257" · 6.53 mm | ⌀ 6.6 | 9/32"0.2813" · 7.14 mm | |
| 3/8"-16 UNC | 16 | 0.375" · 9.525 mm | 5/16"0.3125" · 7.94 mm | ⌀ 8 | 11/32"0.3438" · 8.73 mm | |
| 7/16"-14 UNC | 14 | 0.4375" · 11.113 mm | U0.368" · 9.35 mm | ⌀ 9.3 | Y0.404" · 10.26 mm | |
| 1/2"-13 UNC | 13 | 0.5" · 12.7 mm | 27/64"0.4219" · 10.72 mm | ⌀ 10.8 | 15/32"0.4688" · 11.91 mm | |
| 9/16"-12 UNC | 12 | 0.5625" · 14.288 mm | 31/64"0.4844" · 12.3 mm | ⌀ 12.2 | 33/64"0.5156" · 13.1 mm | |
| 5/8"-11 UNC | 11 | 0.625" · 15.875 mm | 17/32"0.5313" · 13.49 mm | ⌀ 13.5 | 37/64"0.5781" · 14.68 mm | |
| 3/4"-10 UNC | 10 | 0.75" · 19.05 mm | 21/32"0.6563" · 16.67 mm | ⌀ 16.5 | 45/64"0.7031" · 17.86 mm | |
| 7/8"-9 UNC | 9 | 0.875" · 22.225 mm | 49/64"0.7656" · 19.45 mm | ⌀ 19.5 | 13/16"0.8125" · 20.64 mm | |
| 1"-8 UNC | 8 | 1" · 25.4 mm | 7/8"0.875" · 22.23 mm | ⌀ 22.5 | 15/16"0.9375" · 23.81 mm | |
| 1-1/8"-7 UNC | 7 | 1.125" · 28.575 mm | 63/64"0.9844" · 25 mm | ⌀ 25 | 1-3/64"1.0469" · 26.59 mm | |
| 1-1/4"-7 UNC | 7 | 1.25" · 31.75 mm | 1-7/64"1.1094" · 28.18 mm | ⌀ 28 | 1-11/64"1.1719" · 29.77 mm | |
| 1-3/8"-6 UNC | 6 | 1.375" · 34.925 mm | 1-7/32"1.2188" · 30.96 mm | ⌀ 31 | 1-19/64"1.2969" · 32.94 mm | |
| 1-1/2"-6 UNC | 6 | 1.5" · 38.1 mm | 1-11/32"1.3438" · 34.13 mm | ⌀ 34 | 1-27/64"1.4219" · 36.12 mm | |
| 1-3/4"-5 UNC | 5 | 1.75" · 44.45 mm | 1-9/16"1.5625" · 39.69 mm | ⌀ 39.5 | 1-21/32"1.6563" · 42.07 mm | |
| 2"-4.5 UNC | 4.5 | 2" · 50.8 mm | 1-25/32"1.7813" · 45.24 mm | ⌀ 45.5 | 1-57/64"1.8906" · 48.02 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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