Tap Drill Chart
Look up verified recommended drill bit sizes for standard Unified Inch (UNC coarse, UNF fine) and ISO Metric threads before tapping.
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Standard Tap Drill Reference Tables
Standard Tap Drill Chart
Imperial UNC, UNF, and Metric Standard Cutting Tap Drill Hole Recommendations (~75% Thread Depth)
| Thread Size | Series | Pitch / TPI | Major Dia (in) | Major Dia (mm) | Recommended Drill | Drill Dia (in) | Drill Dia (mm) | Copy |
|---|---|---|---|---|---|---|---|---|
| #1-64 UNC | UNC | 64 TPI | 0.0730" | 1.854 mm | #53 | 0.0595" | 1.511 mm | |
| #2-56 UNC | UNC | 56 TPI | 0.0860" | 2.184 mm | #50 | 0.0700" | 1.778 mm | |
| #3-48 UNC | UNC | 48 TPI | 0.0990" | 2.515 mm | #47 | 0.0785" | 1.994 mm | |
| #4-40 UNC | UNC | 40 TPI | 0.1120" | 2.845 mm | #43 | 0.0890" | 2.261 mm | |
| #5-40 UNC | UNC | 40 TPI | 0.1250" | 3.175 mm | #38 | 0.1015" | 2.578 mm | |
| #6-32 UNC | UNC | 32 TPI | 0.1380" | 3.505 mm | #36 | 0.1065" | 2.705 mm | |
| #8-32 UNC | UNC | 32 TPI | 0.1640" | 4.166 mm | #29 | 0.1360" | 3.454 mm | |
| #10-24 UNC | UNC | 24 TPI | 0.1900" | 4.826 mm | #25 | 0.1495" | 3.797 mm | |
| #12-24 UNC | UNC | 24 TPI | 0.2160" | 5.486 mm | #16 | 0.1770" | 4.496 mm | |
| 1/4"-20 UNC | UNC | 20 TPI | 0.2500" | 6.35 mm | #7 | 0.2010" | 5.105 mm | |
| 5/16"-18 UNC | UNC | 18 TPI | 0.3125" | 7.938 mm | F | 0.2570" | 6.528 mm | |
| 3/8"-16 UNC | UNC | 16 TPI | 0.3750" | 9.525 mm | 5/16" | 0.3125" | 7.938 mm | |
| 7/16"-14 UNC | UNC | 14 TPI | 0.4375" | 11.113 mm | U | 0.3680" | 9.347 mm | |
| 1/2"-13 UNC | UNC | 13 TPI | 0.5000" | 12.70 mm | 27/64" | 0.4219" | 10.716 mm | |
| 9/16"-12 UNC | UNC | 12 TPI | 0.5625" | 14.287 mm | 31/64" | 0.4844" | 12.303 mm | |
| 5/8"-11 UNC | UNC | 11 TPI | 0.6250" | 15.875 mm | 17/32" | 0.5313" | 13.494 mm | |
| 3/4"-10 UNC | UNC | 10 TPI | 0.7500" | 19.05 mm | 21/32" | 0.6563" | 16.669 mm | |
| 7/8"-9 UNC | UNC | 9 TPI | 0.8750" | 22.225 mm | 49/64" | 0.7656" | 19.447 mm | |
| 1"-8 UNC | UNC | 8 TPI | 1.0000" | 25.40 mm | 7/8" | 0.8750" | 22.225 mm | |
| 1-1/8"-7 UNC | UNC | 7 TPI | 1.1250" | 28.575 mm | 63/64" | 0.9844" | 25.003 mm | |
| #0-80 UNF | UNF | 80 TPI | 0.0600" | 1.524 mm | #56 | 0.0465" | 1.181 mm | |
| #1-72 UNF | UNF | 72 TPI | 0.0730" | 1.854 mm | #53 | 0.0595" | 1.511 mm | |
| #2-64 UNF | UNF | 64 TPI | 0.0860" | 2.184 mm | #50 | 0.0700" | 1.778 mm | |
| #3-56 UNF | UNF | 56 TPI | 0.0990" | 2.515 mm | #45 | 0.0820" | 2.083 mm | |
| #4-48 UNF | UNF | 48 TPI | 0.1120" | 2.845 mm | #42 | 0.0935" | 2.375 mm | |
| #5-44 UNF | UNF | 44 TPI | 0.1250" | 3.175 mm | #37 | 0.1040" | 2.642 mm | |
| #6-40 UNF | UNF | 40 TPI | 0.1380" | 3.505 mm | #33 | 0.1130" | 2.87 mm | |
| #8-36 UNF | UNF | 36 TPI | 0.1640" | 4.166 mm | #29 | 0.1360" | 3.454 mm | |
| #10-32 UNF | UNF | 32 TPI | 0.1900" | 4.826 mm | #21 | 0.1590" | 4.039 mm | |
| #12-28 UNF | UNF | 28 TPI | 0.2160" | 5.486 mm | #14 | 0.1820" | 4.623 mm | |
| 1/4"-28 UNF | UNF | 28 TPI | 0.2500" | 6.35 mm | #3 | 0.2130" | 5.41 mm | |
| 5/16"-24 UNF | UNF | 24 TPI | 0.3125" | 7.938 mm | I | 0.2720" | 6.909 mm | |
| 3/8"-24 UNF | UNF | 24 TPI | 0.3750" | 9.525 mm | Q | 0.3320" | 8.433 mm | |
| 7/16"-20 UNF | UNF | 20 TPI | 0.4375" | 11.113 mm | 25/64" | 0.3906" | 9.922 mm | |
| 1/2"-20 UNF | UNF | 20 TPI | 0.5000" | 12.70 mm | 29/64" | 0.4531" | 11.509 mm | |
| 9/16"-18 UNF | UNF | 18 TPI | 0.5625" | 14.287 mm | 33/64" | 0.5156" | 13.097 mm | |
| 5/8"-18 UNF | UNF | 18 TPI | 0.6250" | 15.875 mm | 37/64" | 0.5781" | 14.684 mm | |
| 3/4"-16 UNF | UNF | 16 TPI | 0.7500" | 19.05 mm | 11/16" | 0.6875" | 17.462 mm | |
| 7/8"-14 UNF | UNF | 14 TPI | 0.8750" | 22.225 mm | 13/16" | 0.8125" | 20.637 mm | |
| 1"-12 UNF | UNF | 12 TPI | 1.0000" | 25.40 mm | 59/64" | 0.9219" | 23.416 mm | |
| 1"-14 UNS / Special Fine | UNF / UNS | 14 TPI | 1.0000" | 25.40 mm | 15/16" | 0.9375" | 23.813 mm | |
| M1.6 × 0.35 | Metric Coarse | 0.35 mm | 0.0630" | 1.60 mm | 1.25 mm | 0.0492" | 1.25 mm | |
| M2 × 0.4 | Metric Coarse | 0.40 mm | 0.0787" | 2.00 mm | 1.60 mm | 0.0630" | 1.60 mm | |
| M2.5 × 0.45 | Metric Coarse | 0.45 mm | 0.0984" | 2.50 mm | 2.05 mm | 0.0807" | 2.05 mm | |
| M3 × 0.5 | Metric Coarse | 0.50 mm | 0.1181" | 3.00 mm | 2.50 mm | 0.0984" | 2.50 mm | |
| M3.5 × 0.6 | Metric Coarse | 0.60 mm | 0.1378" | 3.50 mm | 2.90 mm | 0.1142" | 2.90 mm | |
| M4 × 0.7 | Metric Coarse | 0.70 mm | 0.1575" | 4.00 mm | 3.30 mm | 0.1299" | 3.30 mm | |
| M5 × 0.8 | Metric Coarse | 0.80 mm | 0.1969" | 5.00 mm | 4.20 mm | 0.1654" | 4.20 mm | |
| M6 × 1.0 | Metric Coarse | 1.00 mm | 0.2362" | 6.00 mm | 5.00 mm | 0.1969" | 5.00 mm | |
| M7 × 1.0 | Metric Coarse | 1.00 mm | 0.2756" | 7.00 mm | 6.00 mm | 0.2362" | 6.00 mm | |
| M8 × 1.25 | Metric Coarse | 1.25 mm | 0.3150" | 8.00 mm | 6.80 mm | 0.2677" | 6.80 mm | |
| M10 × 1.5 | Metric Coarse | 1.50 mm | 0.3937" | 10.00 mm | 8.50 mm | 0.3346" | 8.50 mm | |
| M12 × 1.75 | Metric Coarse | 1.75 mm | 0.4724" | 12.00 mm | 10.20 mm | 0.4016" | 10.20 mm | |
| M14 × 2.0 | Metric Coarse | 2.00 mm | 0.5512" | 14.00 mm | 12.00 mm | 0.4724" | 12.00 mm | |
| M16 × 2.0 | Metric Coarse | 2.00 mm | 0.6299" | 16.00 mm | 14.00 mm | 0.5512" | 14.00 mm | |
| M18 × 2.5 | Metric Coarse | 2.50 mm | 0.7087" | 18.00 mm | 15.50 mm | 0.6102" | 15.50 mm | |
| M20 × 2.5 | Metric Coarse | 2.50 mm | 0.7874" | 20.00 mm | 17.50 mm | 0.6890" | 17.50 mm | |
| M22 × 2.5 | Metric Coarse | 2.50 mm | 0.8661" | 22.00 mm | 19.50 mm | 0.7677" | 19.50 mm | |
| M24 × 3.0 | Metric Coarse | 3.00 mm | 0.9449" | 24.00 mm | 21.00 mm | 0.8268" | 21.00 mm | |
| M8 × 1.0 | Metric Fine | 1.00 mm | 0.3150" | 8.00 mm | 7.00 mm | 0.2756" | 7.00 mm | |
| M10 × 1.0 | Metric Fine | 1.00 mm | 0.3937" | 10.00 mm | 9.00 mm | 0.3543" | 9.00 mm | |
| M10 × 1.25 | Metric Fine | 1.25 mm | 0.3937" | 10.00 mm | 8.80 mm | 0.3465" | 8.80 mm | |
| M12 × 1.25 | Metric Fine | 1.25 mm | 0.4724" | 12.00 mm | 10.80 mm | 0.4252" | 10.80 mm | |
| M12 × 1.5 | Metric Fine | 1.50 mm | 0.4724" | 12.00 mm | 10.50 mm | 0.4134" | 10.50 mm | |
| M14 × 1.5 | Metric Fine | 1.50 mm | 0.5512" | 14.00 mm | 12.50 mm | 0.4921" | 12.50 mm | |
| M16 × 1.5 | Metric Fine | 1.50 mm | 0.6299" | 16.00 mm | 14.50 mm | 0.5709" | 14.50 mm | |
| M18 × 1.5 | Metric Fine | 1.50 mm | 0.7087" | 18.00 mm | 16.50 mm | 0.6496" | 16.50 mm | |
| M20 × 1.5 | Metric Fine | 1.50 mm | 0.7874" | 20.00 mm | 18.50 mm | 0.7283" | 18.50 mm |
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What Does a Tap Drill Size Mean?
A tap drill creates the hole in a workpiece prior to cutting or forming internal screw threads. The hole diameter must be smaller than the thread's major (outside) diameter, but large enough that the tap's cutting teeth do not bind, break, or create excessive friction.
Standard tap drill charts are calculated to produce approximately 70% to 75% theoretical thread depth. Engineering research has shown that a 75% thread depth provides over 95% of the ultimate holding strength of a 100% full thread, while significantly reducing tapping torque and tool breakage.
Cutting Taps vs. Forming (Roll) Taps
Cutting Taps: Remove material as chips. The values shown in the charts above represent standard cutting taps.
Important Caveat for Forming/Roll Taps: Thread-forming (fluteless/roll) taps displace and cold-form metal rather than cutting chips. Forming taps require significantly larger pre-drilled hole diameters. Do not use standard cutting-tap drill sizes for roll-forming taps.
Why Recommended Tap Hole Sizes Can Vary
- Workpiece Material: Hard, tough materials (such as stainless steels, titanium, or nickel alloys) often benefit from a slightly larger tap drill hole (around 60%–65% thread depth) to prevent tap seizure and breakage. Softer materials (like aluminum or mild steel) can easily accept 75% thread depth.
- Engagement Length: When thread engagement depth exceeds 1.5 times the fastener diameter, lower percentage thread engagement (60%–65%) is generally recommended because holding strength is distributed across more threads.
- Deep Blind Holes: For deep blind holes, chip packing can cause high torque; ensure adequate drill depth beyond the required full thread depth.
Thread Standards & Reference Basis
View Full Methodology →- ASME B1.1 – Unified Inch Screw Threads (UN and UNR Thread Form): Standard dimensions and tolerances for Unified Coarse (UNC) and Unified Fine (UNF) inch screw threads.
- ISO 261 / ISO 68-1 – ISO General Purpose Metric Screw Threads: General metric screw thread profile (M profile) standardizing nominal diameter and pitch combinations.
- Machinery's Handbook (31st Edition): Standard reference work for mechanical engineers, designers, manufacturing engineers, and machinists.
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