Tap Drill Chart for Numbered Screw Sizes (#0 to #12)
Numbered machine screw sizes use number drills. Two screw numbers come in a coarse and a fine thread: #6-32 and #6-40, and #10-24 and #10-32.
| Thread | Series | Major diameter | Pitch | Aluminum, brass (75%) | Mild steel (60%) | Stainless, titanium (50%) |
|---|---|---|---|---|---|---|
| #0-80 | UNF | 0.0600 in (1.52 mm) | 80 TPI (0.318 mm) | 3/64 in 81% | 3/64 in 81% | #55 49% |
| #2-56 | UNC | 0.0860 in (2.18 mm) | 56 TPI (0.454 mm) | #50 69% | #49 56% | #49 56% |
| #4-40 | UNC | 0.1120 in (2.84 mm) | 40 TPI (0.635 mm) | #43 71% | #42 57% | #41 49% |
| #5-40 | UNC | 0.1250 in (3.17 mm) | 40 TPI (0.635 mm) | #38 72% | #37 65% | 7/64 in 48% |
| #6-32 | UNC | 0.1380 in (3.51 mm) | 32 TPI (0.794 mm) | #36 78% | #33 62% | #32 54% |
| #6-40 | UNF | 0.1380 in (3.51 mm) | 40 TPI (0.635 mm) | #33 77% | #31 55% | #31 55% |
| #8-32 | UNC | 0.1640 in (4.17 mm) | 32 TPI (0.794 mm) | #29 69% | #28 58% | #27 49% |
| #10-24 | UNC | 0.1900 in (4.83 mm) | 24 TPI (1.058 mm) | #25 75% | #22 61% | #20 54% |
| #10-32 | UNF | 0.1900 in (4.83 mm) | 32 TPI (0.794 mm) | #21 76% | #19 59% | #18 50% |
| #12-24 | UNC | 0.2160 in (5.49 mm) | 24 TPI (1.058 mm) | #16 72% | #14 63% | #12 50% |
Small percentages show the thread engagement each drill leaves. Click a thread for the full page.
Tap Drill Chart for Numbered Screw Sizes (#0 to #12) | tapdrillsize.com/screw-size-tap-drill-chart/ | Last reviewed October 7, 2026 | Check your tap maker's chart before cutting.
How screw numbers work
A screw number sets the major diameter: 0.060 in plus 0.013 in for each number. #10 is 0.060 + 0.013 x 10 = 0.1900 in.
| Screw | Formula | Major diameter | In mm | Threads here |
|---|---|---|---|---|
| #0 | 0.060 + 0.013 x 0 | 0.0600 in | 1.52 mm | #0-80 |
| #2 | 0.060 + 0.013 x 2 | 0.0860 in | 2.18 mm | #2-56 |
| #4 | 0.060 + 0.013 x 4 | 0.1120 in | 2.84 mm | #4-40 |
| #5 | 0.060 + 0.013 x 5 | 0.1250 in | 3.17 mm | #5-40 |
| #6 | 0.060 + 0.013 x 6 | 0.1380 in | 3.51 mm | #6-32, #6-40 |
| #8 | 0.060 + 0.013 x 8 | 0.1640 in | 4.17 mm | #8-32 |
| #10 | 0.060 + 0.013 x 10 | 0.1900 in | 4.83 mm | #10-24, #10-32 |
| #12 | 0.060 + 0.013 x 12 | 0.2160 in | 5.49 mm | #12-24 |
Same number, two pitches
Two screw numbers come in a coarse and a fine thread at the same diameter. They need different drills.
Screw sizes and their metric lookalikes
Each screw number has a metric size close to it. The pitch differs, so they are not interchangeable.
| Screw | Diameter | Closest metric size | Difference | Screw pitch | Metric pitch |
|---|---|---|---|---|---|
| #0 | 1.52 mm | M2 | 0.48 mm | 0.318 mm | 0.40 mm |
| #2 | 2.18 mm | M2 | 0.18 mm | 0.454 mm | 0.40 mm |
| #4 | 2.84 mm | M3 | 0.16 mm | 0.635 mm | 0.50 mm |
| #5 | 3.17 mm | M3 | 0.17 mm | 0.635 mm | 0.50 mm |
| #6 | 3.51 mm | M3.5 | 0.01 mm | 0.794 mm | 0.60 mm |
| #8 | 4.17 mm | M4 | 0.17 mm | 0.794 mm | 0.70 mm |
| #10 | 4.83 mm | M5 | 0.17 mm | 1.058 mm | 0.80 mm |
| #12 | 5.49 mm | M5 | 0.49 mm | 1.058 mm | 0.80 mm |
Coarse or fine thread
A coarse thread is deeper. A full #6-32 thread is 0.0203 in deep on each side and a full #6-40 thread is 0.0162 in deep. A full #10-24 thread is 0.0271 in deep and #10-32 is 0.0203 in deep.
A shallower thread leaves less metal to cut, so the fine thread takes the bigger drill: #33 for #6-40 against #36 for #6-32.
Drills for small taps
ToolGrit suggests 50 to 55% thread for small taps (#6 and below), which are easy to break. These are the drills nearest 55% and 50% for those sizes.
| Thread | Drill near 55% | Thread left | Drill near 50% | Thread left |
|---|---|---|---|---|
| #0-80 | 3/64 in | 81% | #55 | 49% |
| #2-56 | #49 | 56% | #49 | 56% |
| #4-40 | 3/32 in | 56% | #41 | 49% |
| #5-40 | #36 | 57% | 7/64 in | 48% |
| #6-32 | #32 | 54% | #32 | 54% |
| #6-40 | #31 | 55% | #31 | 55% |
About number drills
Number drills run from #80, the smallest, up to #1 at 0.2280 in. A bigger number is a smaller drill. The drill size chart lists every number, letter and fractional drill with its diameter. Sizes come from Wikipedia: drill bit sizes.
FAQ
What is the tap drill size for #6-32?
#36 (0.1065 in, 2.71 mm) leaves about 78% thread. The fine #6-40 takes #33.
What size is a #10 screw?
A #10 screw is 0.1900 in across, which is 4.83 mm. Every screw number follows 0.060 in plus 0.013 in times the number.
What are the tap drills for #10-24 and #10-32?
#10-24 takes #25 and #10-32 takes #21. The two screws are the same diameter, so count the threads per inch to tell them apart.
Chart drills match the American Fastener tap and drill chart and the Fabworks tap drill chart. Thread percentages use the formula printed in the OSG tap drill chart, Vol 3 (2024). Last reviewed October 7, 2026. Method: how the numbers are calculated.