Thread and tap drill calculator
Choose a thread type in the tabs below: metric (cutting tap), forming tap, UNC/UNF/UNEF, G, R/Rc/Rp and NPT/NPS pipe threads, trapezoidal Tr, Helicoil and tapping speed. For metric threads you can enter any diameter and pitch to get the minor diameter range and thread-turning infeeds.
- Tap drill diameter (D − P)
- Pitch diameter d2
- External minor diameter d3
- Internal minor diameter D1
- Thread minor diameter range (min – max)
- 8.376 – 8.676 mm (6H)
- External thread depth h3 (radial)
| Pass | Cumulative depth (mm) | Infeed this pass (mm) |
|---|
Forming (chipless) taps suit ductile materials such as aluminum, copper, low-carbon steel and stainless, not cast iron. Values are typical (about D − 0.45 × P); check the tap maker's catalog.
UNC/UNF: theoretical hole for about 65% thread, D − 0.0068 × 65 / TPI (inch).
- Forming tap drill
- Compare: cutting tap drill
- Pitch P (mm)
Standard drills for about 75% thread engagement, shown as inch drill sizes (number, letter, fraction) with mm equivalents. Minor diameter range per class 2B (ASME B1.1).
- Tap drill
- Threads per inch (TPI)
- Pitch
- Major diameter
- Thread minor diameter range (min – max)
G is the ISO 228-1 parallel pipe thread (BSPP); it seals with a washer or gasket, not on the thread.
- Tap drill
- Threads per inch (TPI)
- Pitch
- Major diameter
- G minor diameter range (min – max)
R (external) / Rc (internal) are ISO 7-1 taper pipe threads with a 1:16 taper, sealing on the thread. Drill sizes vary slightly by tap maker (e.g. Rc1/8: 8.1–8.2 mm); use your tap maker's value. Rp is the parallel internal thread that mates with an R external thread; diameter tolerance per ISO 7-1.
- Drill (tap-maker catalogs)
- Threads per inch (TPI)
- Pitch
- Gauge diameter
- Thread minor diameter range (min – max)
NPT is the American taper pipe thread (ASME B1.20.1), 60° angle, with two drill sizes: direct tapping, or a smaller drill followed by a taper reamer. NPS is the American straight pipe thread. Do not mix with R/Rc/G (55°). Drill sizes vary slightly by maker.
- Tap drill
- Drill with taper reamer
- Threads per inch (TPI)
- Pitch
Metric trapezoidal thread per ISO 2904, 30° angle, used for lead screws, vises and presses.
- Internal minor D1 (pre-bore)
- Pitch diameter d2
- External minor d3
- Internal major D4
- Pitch P (mm)
Wire thread inserts (Helicoil) need a larger hole and a dedicated STI tap, not the normal tap drill. Values follow Heli-Coil drilling data; check the catalog for other sizes or brands.
- Drill – aluminum
- Drill – steel, magnesium, plastic
- Drilled hole (min – max)
- STI tap
Vc values are starting points for coated HSS-E taps with cutting oil; forming taps can run about 20% faster (not on cast iron). Blind-hole drill depth = thread depth + 3 pitches (tap chamfer) + 0.3 × drill diameter (118° point). For rigid tapping, F = S × P.
- Recommended Vc
- Spindle speed S
- Feed per rev (= pitch)
- Feed rate F
- Min. drill depth (blind hole)
- FANUC example (G84)
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📘 Free download: CNC machine buyer's guide 2026 (PDF) →- Dimensions follow the ISO 68-1 basic profile. Infeed decreases per pass for equal chip area; the default number of passes is a general reference, so adjust it to your insert maker's recommendation.
Metric coarse tap drill chart M1–M39 (with minor diameter range)
Formula: tap drill = D − P (nominal diameter minus pitch). Example M10 × 1.5: 10 − 1.5 = 8.5 mm. Minor diameter range of the internal thread per ISO 965-1: 6H for most sizes; 5H for M1–M1.4 and pitches 0.25–0.3; 4H for pitch 0.2.
| Size | Tap drill (mm) | Minor min (mm) | Minor max (mm) | Tolerance class |
|---|---|---|---|---|
| M1 × 0.25 | 0.75 | 0.729 | 0.785 | 5H |
| M1.1 × 0.25 | 0.85 | 0.829 | 0.885 | 5H |
| M1.2 × 0.25 | 0.95 | 0.929 | 0.985 | 5H |
| M1.4 × 0.3 | 1.10 | 1.075 | 1.142 | 5H |
| M1.6 × 0.35 | 1.25 | 1.221 | 1.321 | 6H |
| M1.7 × 0.35 (old JIS) | 1.35 | 1.321 | 1.421 | 6H |
| M1.8 × 0.35 | 1.45 | 1.421 | 1.521 | 6H |
| M2 × 0.4 | 1.60 | 1.567 | 1.679 | 6H |
| M2.2 × 0.45 | 1.75 | 1.713 | 1.838 | 6H |
| M2.3 × 0.4 (old JIS) | 1.90 | 1.867 | 1.979 | 6H |
| M2.5 × 0.45 | 2.05 | 2.013 | 2.138 | 6H |
| M2.6 × 0.45 (old JIS) | 2.15 | 2.113 | 2.238 | 6H |
| M3 × 0.5 | 2.50 | 2.459 | 2.599 | 6H |
| M3.5 × 0.6 | 2.90 | 2.850 | 3.010 | 6H |
| M4 × 0.7 | 3.30 | 3.242 | 3.422 | 6H |
| M4.5 × 0.75 | 3.75 | 3.688 | 3.878 | 6H |
| M5 × 0.8 | 4.20 | 4.134 | 4.334 | 6H |
| M6 × 1 | 5.00 | 4.917 | 5.153 | 6H |
| M7 × 1 | 6.00 | 5.917 | 6.153 | 6H |
| M8 × 1.25 | 6.75 | 6.647 | 6.912 | 6H |
| M9 × 1.25 | 7.75 | 7.647 | 7.912 | 6H |
| M10 × 1.5 | 8.50 | 8.376 | 8.676 | 6H |
| M11 × 1.5 | 9.50 | 9.376 | 9.676 | 6H |
| M12 × 1.75 | 10.25 | 10.106 | 10.441 | 6H |
| M14 × 2 | 12.00 | 11.835 | 12.210 | 6H |
| M16 × 2 | 14.00 | 13.835 | 14.210 | 6H |
| M18 × 2.5 | 15.50 | 15.294 | 15.744 | 6H |
| M20 × 2.5 | 17.50 | 17.294 | 17.744 | 6H |
| M22 × 2.5 | 19.50 | 19.294 | 19.744 | 6H |
| M24 × 3 | 21.00 | 20.752 | 21.252 | 6H |
| M27 × 3 | 24.00 | 23.752 | 24.252 | 6H |
| M30 × 3.5 | 26.50 | 26.211 | 26.771 | 6H |
| M33 × 3.5 | 29.50 | 29.211 | 29.771 | 6H |
| M36 × 4 | 32.00 | 31.670 | 32.270 | 6H |
| M39 × 4 | 35.00 | 34.670 | 35.270 | 6H |
Metric fine thread tap drill chart (with minor diameter range)
Metric fine threads: tap drill = nominal diameter − pitch (D − P). Minor diameter range of the internal thread per ISO 965-1: 6H for most sizes; 5H for M1–M1.4 and pitches 0.25–0.3; 4H for pitch 0.2.
| Size | Tap drill (mm) | Minor min (mm) | Minor max (mm) | Tolerance class |
|---|---|---|---|---|
| M1 × 0.2 | 0.80 | 0.783 | 0.821 | 4H |
| M1.1 × 0.2 | 0.90 | 0.883 | 0.921 | 4H |
| M1.2 × 0.2 | 1.00 | 0.983 | 1.021 | 4H |
| M1.4 × 0.2 | 1.20 | 1.183 | 1.221 | 4H |
| M1.6 × 0.2 | 1.40 | 1.383 | 1.421 | 4H |
| M1.8 × 0.2 | 1.60 | 1.583 | 1.621 | 4H |
| M2 × 0.25 | 1.75 | 1.729 | 1.785 | 5H |
| M2.2 × 0.25 | 1.95 | 1.929 | 1.985 | 5H |
| M2.5 × 0.35 | 2.15 | 2.121 | 2.221 | 6H |
| M3 × 0.35 | 2.65 | 2.621 | 2.721 | 6H |
| M3.5 × 0.35 | 3.15 | 3.121 | 3.221 | 6H |
| M4 × 0.5 | 3.50 | 3.459 | 3.599 | 6H |
| M4.5 × 0.5 | 4.00 | 3.959 | 4.099 | 6H |
| M5 × 0.5 | 4.50 | 4.459 | 4.599 | 6H |
| M5.5 × 0.5 | 5.00 | 4.959 | 5.099 | 6H |
| M6 × 0.75 | 5.25 | 5.188 | 5.378 | 6H |
| M7 × 0.75 | 6.25 | 6.188 | 6.378 | 6H |
| M8 × 1 | 7.00 | 6.917 | 7.153 | 6H |
| M8 × 0.75 | 7.25 | 7.188 | 7.378 | 6H |
| M9 × 1 | 8.00 | 7.917 | 8.153 | 6H |
| M9 × 0.75 | 8.25 | 8.188 | 8.378 | 6H |
| M10 × 1.25 | 8.75 | 8.647 | 8.912 | 6H |
| M10 × 1 | 9.00 | 8.917 | 9.153 | 6H |
| M10 × 0.75 | 9.25 | 9.188 | 9.378 | 6H |
| M11 × 1 | 10.00 | 9.917 | 10.153 | 6H |
| M11 × 0.75 | 10.25 | 10.188 | 10.378 | 6H |
| M12 × 1.5 | 10.50 | 10.376 | 10.676 | 6H |
| M12 × 1.25 | 10.75 | 10.647 | 10.912 | 6H |
| M12 × 1 | 11.00 | 10.917 | 11.153 | 6H |
| M14 × 1.5 | 12.50 | 12.376 | 12.676 | 6H |
| M14 × 1 | 13.00 | 12.917 | 13.153 | 6H |
| M15 × 1.5 | 13.50 | 13.376 | 13.676 | 6H |
| M15 × 1 | 14.00 | 13.917 | 14.153 | 6H |
| M16 × 1.5 | 14.50 | 14.376 | 14.676 | 6H |
| M16 × 1 | 15.00 | 14.917 | 15.153 | 6H |
| M17 × 1.5 | 15.50 | 15.376 | 15.676 | 6H |
| M17 × 1 | 16.00 | 15.917 | 16.153 | 6H |
| M18 × 2 | 16.00 | 15.835 | 16.210 | 6H |
| M18 × 1.5 | 16.50 | 16.376 | 16.676 | 6H |
| M18 × 1 | 17.00 | 16.917 | 17.153 | 6H |
| M20 × 2 | 18.00 | 17.835 | 18.210 | 6H |
| M20 × 1.5 | 18.50 | 18.376 | 18.676 | 6H |
| M20 × 1 | 19.00 | 18.917 | 19.153 | 6H |
| M22 × 2 | 20.00 | 19.835 | 20.210 | 6H |
| M22 × 1.5 | 20.50 | 20.376 | 20.676 | 6H |
| M22 × 1 | 21.00 | 20.917 | 21.153 | 6H |
| M24 × 2 | 22.00 | 21.835 | 22.210 | 6H |
| M24 × 1.5 | 22.50 | 22.376 | 22.676 | 6H |
| M24 × 1 | 23.00 | 22.917 | 23.153 | 6H |
| M27 × 2 | 25.00 | 24.835 | 25.210 | 6H |
| M27 × 1.5 | 25.50 | 25.376 | 25.676 | 6H |
| M30 × 2 | 28.00 | 27.835 | 28.210 | 6H |
| M30 × 1.5 | 28.50 | 28.376 | 28.676 | 6H |
| M33 × 2 | 31.00 | 30.835 | 31.210 | 6H |
| M33 × 1.5 | 31.50 | 31.376 | 31.676 | 6H |
| M36 × 3 | 33.00 | 32.752 | 33.252 | 6H |
| M36 × 2 | 34.00 | 33.835 | 34.210 | 6H |
| M36 × 1.5 | 34.50 | 34.376 | 34.676 | 6H |
| M39 × 3 | 36.00 | 35.752 | 36.252 | 6H |
| M39 × 2 | 37.00 | 36.835 | 37.210 | 6H |
Forming tap drill chart (metric coarse)
Forming (chipless) taps suit ductile materials such as aluminum, copper, low-carbon steel and stainless, not cast iron. Values are typical (about D − 0.45 × P); check the tap maker's catalog.
| Size | Forming tap drill (mm) | Compare: cutting tap drill (mm) |
|---|---|---|
| M1 × 0.25 | 0.90 | 0.75 |
| M1.1 × 0.25 | 1.00 | 0.85 |
| M1.2 × 0.25 | 1.10 | 0.95 |
| M1.4 × 0.3 | 1.25 | 1.10 |
| M1.6 × 0.35 | 1.45 | 1.25 |
| M1.8 × 0.35 | 1.65 | 1.45 |
| M2 × 0.4 | 1.80 | 1.60 |
| M2.2 × 0.45 | 2.00 | 1.75 |
| M2.5 × 0.45 | 2.30 | 2.05 |
| M3 × 0.5 | 2.80 | 2.50 |
| M3.5 × 0.6 | 3.25 | 2.90 |
| M4 × 0.7 | 3.70 | 3.30 |
| M4.5 × 0.75 | 4.15 | 3.75 |
| M5 × 0.8 | 4.65 | 4.20 |
| M6 × 1 | 5.55 | 5.00 |
| M7 × 1 | 6.55 | 6.00 |
| M8 × 1.25 | 7.40 | 6.75 |
| M9 × 1.25 | 8.45 | 7.75 |
| M10 × 1.5 | 9.30 | 8.50 |
| M11 × 1.5 | 10.35 | 9.50 |
| M12 × 1.75 | 11.20 | 10.25 |
| M14 × 2 | 13.10 | 12.00 |
| M16 × 2 | 15.10 | 14.00 |
| M18 × 2.5 | 16.90 | 15.50 |
| M20 × 2.5 | 18.90 | 17.50 |
| M22 × 2.5 | 20.90 | 19.50 |
| M24 × 3 | 22.60 | 21.00 |
Forming tap drill chart (metric fine)
Values from the Haas roll-tap chart; sizes not listed there use about 65% thread (D − 65 × P / 147.06), rounded down to 0.1 mm.
| Size | Forming tap drill (mm) | Compare: cutting tap drill (mm) |
|---|---|---|
| M1 × 0.2 | 0.90 | 0.80 |
| M1.1 × 0.2 | 1.00 | 0.90 |
| M1.2 × 0.2 | 1.10 | 1.00 |
| M1.4 × 0.2 | 1.30 | 1.20 |
| M1.6 × 0.2 | 1.50 | 1.40 |
| M1.8 × 0.2 | 1.70 | 1.60 |
| M2 × 0.25 | 1.90 | 1.75 |
| M2.2 × 0.25 | 2.10 | 1.95 |
| M2.5 × 0.35 | 2.35 | 2.15 |
| M3 × 0.35 | 2.85 | 2.65 |
| M3.5 × 0.35 | 3.35 | 3.15 |
| M4 × 0.5 | 3.80 | 3.50 |
| M4.5 × 0.5 | 4.30 | 4.00 |
| M5 × 0.5 | 4.80 | 4.50 |
| M5.5 × 0.5 | 5.30 | 5.00 |
| M6 × 0.75 | 5.65 | 5.25 |
| M7 × 0.75 | 6.65 | 6.25 |
| M8 × 1 | 7.50 | 7.00 |
| M8 × 0.75 | 7.65 | 7.25 |
| M9 × 1 | 8.55 | 8.00 |
| M9 × 0.75 | 8.65 | 8.25 |
| M10 × 1.25 | 9.40 | 8.75 |
| M10 × 1 | 9.50 | 9.00 |
| M10 × 0.75 | 9.65 | 9.25 |
| M11 × 1 | 10.55 | 10.00 |
| M11 × 0.75 | 10.65 | 10.25 |
| M12 × 1.5 | 11.30 | 10.50 |
| M12 × 1.25 | 11.40 | 10.75 |
| M12 × 1 | 11.50 | 11.00 |
| M14 × 1.5 | 13.30 | 12.50 |
| M14 × 1 | 13.55 | 13.00 |
| M15 × 1.5 | 14.35 | 13.50 |
| M15 × 1 | 14.55 | 14.00 |
| M16 × 1.5 | 15.30 | 14.50 |
| M16 × 1 | 15.55 | 15.00 |
| M17 × 1.5 | 16.35 | 15.50 |
| M17 × 1 | 16.55 | 16.00 |
| M18 × 2 | 17.10 | 16.00 |
| M18 × 1.5 | 17.30 | 16.50 |
| M18 × 1 | 17.55 | 17.00 |
| M20 × 2 | 19.10 | 18.00 |
| M20 × 1.5 | 19.30 | 18.50 |
| M20 × 1 | 19.55 | 19.00 |
| M22 × 2 | 21.10 | 20.00 |
| M22 × 1.5 | 21.30 | 20.50 |
| M22 × 1 | 21.55 | 21.00 |
| M24 × 2 | 23.10 | 22.00 |
| M24 × 1.5 | 23.30 | 22.50 |
| M24 × 1 | 23.55 | 23.00 |
Forming tap hole sizes (UNC / UNF)
UNC/UNF: theoretical hole for about 65% thread, D − 0.0068 × 65 / TPI (inch).
| Series | Size | TPI | Forming tap drill (in) | Forming tap drill (mm) |
|---|---|---|---|---|
| UNC | #1-64 | 64 | 0.0661 | 1.68 |
| UNC | #2-56 | 56 | 0.0781 | 1.98 |
| UNC | #3-48 | 48 | 0.0898 | 2.28 |
| UNC | #4-40 | 40 | 0.1009 | 2.56 |
| UNC | #5-40 | 40 | 0.1139 | 2.89 |
| UNC | #6-32 | 32 | 0.1242 | 3.15 |
| UNC | #8-32 | 32 | 0.1502 | 3.81 |
| UNC | #10-24 | 24 | 0.1716 | 4.36 |
| UNC | #12-24 | 24 | 0.1976 | 5.02 |
| UNC | 1/4-20 | 20 | 0.2279 | 5.79 |
| UNC | 5/16-18 | 18 | 0.2879 | 7.31 |
| UNC | 3/8-16 | 16 | 0.3474 | 8.82 |
| UNC | 7/16-14 | 14 | 0.4059 | 10.31 |
| UNC | 1/2-13 | 13 | 0.4660 | 11.84 |
| UNC | 9/16-12 | 12 | 0.5257 | 13.35 |
| UNC | 5/8-11 | 11 | 0.5848 | 14.85 |
| UNC | 3/4-10 | 10 | 0.7058 | 17.93 |
| UNC | 7/8-9 | 9 | 0.8259 | 20.98 |
| UNC | 1-8 | 8 | 0.9447 | 24.00 |
| UNC | 1-1/8-7 | 7 | 1.0619 | 26.97 |
| UNC | 1-1/4-7 | 7 | 1.1869 | 30.15 |
| UNC | 1-3/8-6 | 6 | 1.3013 | 33.05 |
| UNC | 1-1/2-6 | 6 | 1.4263 | 36.23 |
| UNC | 1-3/4-5 | 5 | 1.6616 | 42.20 |
| UNF | #0-80 | 80 | 0.0545 | 1.38 |
| UNF | #1-72 | 72 | 0.0669 | 1.70 |
| UNF | #2-64 | 64 | 0.0791 | 2.01 |
| UNF | #3-56 | 56 | 0.0911 | 2.31 |
| UNF | #4-48 | 48 | 0.1028 | 2.61 |
| UNF | #5-44 | 44 | 0.1150 | 2.92 |
| UNF | #6-40 | 40 | 0.1270 | 3.22 |
| UNF | #8-36 | 36 | 0.1517 | 3.85 |
| UNF | #10-32 | 32 | 0.1762 | 4.48 |
| UNF | #12-28 | 28 | 0.2002 | 5.09 |
| UNF | 1/4-28 | 28 | 0.2342 | 5.95 |
| UNF | 5/16-24 | 24 | 0.2941 | 7.47 |
| UNF | 3/8-24 | 24 | 0.3566 | 9.06 |
| UNF | 7/16-20 | 20 | 0.4154 | 10.55 |
| UNF | 1/2-20 | 20 | 0.4779 | 12.14 |
| UNF | 9/16-18 | 18 | 0.5379 | 13.66 |
| UNF | 5/8-18 | 18 | 0.6004 | 15.25 |
| UNF | 3/4-16 | 16 | 0.7224 | 18.35 |
| UNF | 7/8-14 | 14 | 0.8434 | 21.42 |
| UNF | 1-12 | 12 | 0.9632 | 24.46 |
| UNF | 1-1/8-12 | 12 | 1.0882 | 27.64 |
| UNF | 1-1/4-12 | 12 | 1.2132 | 30.81 |
| UNF | 1-3/8-12 | 12 | 1.3382 | 33.99 |
| UNF | 1-1/2-12 | 12 | 1.4632 | 37.16 |
UNC / UNF tap drill chart
Standard drills for about 75% thread engagement, shown as inch drill sizes (number, letter, fraction) with mm equivalents. Minor diameter range per class 2B (ASME B1.1).
| Series | Size | TPI | Tap drill | Tap drill (mm) | Minor min (mm) | Minor max (mm) |
|---|---|---|---|---|---|---|
| UNC | #1-64 | 64 | #53 | 1.511 | 1.425 | 1.580 |
| UNC | #2-56 | 56 | #50 | 1.778 | 1.694 | 1.872 |
| UNC | #3-48 | 48 | #47 | 1.994 | 1.941 | 2.146 |
| UNC | #4-40 | 40 | #43 | 2.261 | 2.156 | 2.385 |
| UNC | #5-40 | 40 | #38 | 2.578 | 2.487 | 2.697 |
| UNC | #6-32 | 32 | #36 | 2.705 | 2.642 | 2.896 |
| UNC | #8-32 | 32 | #29 | 3.454 | 3.302 | 3.531 |
| UNC | #10-24 | 24 | #25 | 3.797 | 3.683 | 3.937 |
| UNC | #12-24 | 24 | #16 | 4.496 | 4.343 | 4.597 |
| UNC | 1/4-20 | 20 | #7 | 5.105 | 4.978 | 5.258 |
| UNC | 5/16-18 | 18 | F | 6.528 | 6.401 | 6.731 |
| UNC | 3/8-16 | 16 | 5/16 | 7.938 | 7.798 | 8.153 |
| UNC | 7/16-14 | 14 | U | 9.347 | 9.144 | 9.550 |
| UNC | 1/2-13 | 13 | 27/64 | 10.716 | 10.592 | 11.024 |
| UNC | 9/16-12 | 12 | 31/64 | 12.303 | 11.989 | 12.446 |
| UNC | 5/8-11 | 11 | 17/32 | 13.494 | 13.386 | 13.868 |
| UNC | 3/4-10 | 10 | 21/32 | 16.669 | 16.307 | 16.840 |
| UNC | 7/8-9 | 9 | 49/64 | 19.447 | 19.177 | 19.761 |
| UNC | 1-8 | 8 | 7/8 | 22.225 | 21.971 | 22.606 |
| UNC | 1-1/8-7 | 7 | 63/64 | 25.003 | 24.638 | 25.349 |
| UNC | 1-1/4-7 | 7 | 1-7/64 | 28.178 | 27.813 | 28.524 |
| UNC | 1-3/8-6 | 6 | 1-7/32 | 30.956 | 30.353 | 31.115 |
| UNC | 1-1/2-6 | 6 | 1-11/32 | 34.131 | 33.528 | 34.290 |
| UNC | 1-3/4-5 | 5 | 1-9/16 | 39.688 | 38.938 | 39.802 |
| UNF | #0-80 | 80 | 3/64 | 1.191 | 1.181 | 1.306 |
| UNF | #1-72 | 72 | #53 | 1.511 | 1.473 | 1.610 |
| UNF | #2-64 | 64 | #50 | 1.778 | 1.755 | 1.910 |
| UNF | #3-56 | 56 | #45 | 2.083 | 2.024 | 2.197 |
| UNF | #4-48 | 48 | #42 | 2.375 | 2.271 | 2.459 |
| UNF | #5-44 | 44 | #37 | 2.642 | 2.550 | 2.741 |
| UNF | #6-40 | 40 | #33 | 2.870 | 2.819 | 3.023 |
| UNF | #8-36 | 36 | #29 | 3.454 | 3.404 | 3.607 |
| UNF | #10-32 | 32 | #21 | 4.039 | 3.962 | 4.166 |
| UNF | #12-28 | 28 | #14 | 4.623 | 4.496 | 4.724 |
| UNF | 1/4-28 | 28 | #3 | 5.410 | 5.359 | 5.588 |
| UNF | 5/16-24 | 24 | I | 6.909 | 6.782 | 7.036 |
| UNF | 3/8-24 | 24 | Q | 8.433 | 8.382 | 8.636 |
| UNF | 7/16-20 | 20 | 25/64 | 9.922 | 9.728 | 10.033 |
| UNF | 1/2-20 | 20 | 29/64 | 11.509 | 11.328 | 11.608 |
| UNF | 9/16-18 | 18 | 33/64 | 13.097 | 12.751 | 13.081 |
| UNF | 5/8-18 | 18 | 37/64 | 14.684 | 14.351 | 14.681 |
| UNF | 3/4-16 | 16 | 11/16 | 17.463 | 17.323 | 17.678 |
| UNF | 7/8-14 | 14 | 13/16 | 20.638 | 20.269 | 20.650 |
| UNF | 1-12 | 12 | 59/64 | 23.416 | 23.114 | 23.571 |
| UNF | 1-1/8-12 | 12 | 1-3/64 | 26.591 | 26.289 | 26.746 |
| UNF | 1-1/4-12 | 12 | 1-11/64 | 29.766 | 29.464 | 29.921 |
| UNF | 1-3/8-12 | 12 | 1-19/64 | 32.941 | 32.639 | 33.096 |
| UNF | 1-1/2-12 | 12 | 1-27/64 | 36.116 | 35.814 | 36.271 |
UNEF (extra-fine) tap drill chart
Standard drills for about 75% thread engagement, shown as inch drill sizes (number, letter, fraction) with mm equivalents. Minor diameter range per class 2B (ASME B1.1).
| Series | Size | TPI | Tap drill | Tap drill (mm) | Minor min (mm) | Minor max (mm) |
|---|---|---|---|---|---|---|
| UNEF | #12-32 | 32 | #13 | 4.699 | 4.623 | 4.801 |
| UNEF | 1/4-32 | 32 | 7/32 | 5.556 | 5.486 | 5.690 |
| UNEF | 5/16-32 | 32 | 9/32 | 7.144 | 7.087 | 7.264 |
| UNEF | 3/8-32 | 32 | 11/32 | 8.731 | 8.661 | 8.865 |
| UNEF | 7/16-28 | 28 | 13/32 | 10.319 | 10.135 | 10.338 |
| UNEF | 1/2-28 | 28 | 15/32 | 11.906 | 11.709 | 11.938 |
| UNEF | 9/16-24 | 24 | Ø13.2 mm | 13.200 | 13.132 | 13.386 |
| UNEF | 5/8-24 | 24 | Ø14.8 mm | 14.800 | 14.732 | 14.986 |
| UNEF | 11/16-24 | 24 | Ø16.4 mm | 16.400 | 16.307 | 16.561 |
| UNEF | 3/4-20 | 20 | 45/64 | 17.859 | 17.678 | 17.958 |
| UNEF | 13/16-20 | 20 | 49/64 | 19.447 | 19.253 | 19.558 |
| UNEF | 7/8-20 | 20 | 53/64 | 21.034 | 20.853 | 21.133 |
| UNEF | 15/16-20 | 20 | 57/64 | 22.622 | 22.428 | 22.733 |
| UNEF | 1-20 | 20 | 61/64 | 24.209 | 24.028 | 24.308 |
American numbered and fractional screw sizes: major diameter
| Size | Major diameter (inch) | Major diameter (mm) |
|---|---|---|
| No.0 | 0.0600 | 1.524 |
| No.1 | 0.0730 | 1.854 |
| No.2 | 0.0860 | 2.184 |
| No.3 | 0.0990 | 2.515 |
| No.4 | 0.1120 | 2.845 |
| No.5 | 0.1250 | 3.175 |
| No.6 | 0.1380 | 3.505 |
| No.8 | 0.1640 | 4.166 |
| No.10 | 0.1900 | 4.826 |
| No.12 | 0.2160 | 5.486 |
| 1/4 | 0.2500 | 6.350 |
| 5/16 | 0.3125 | 7.938 |
| 3/8 | 0.3750 | 9.525 |
| 7/16 | 0.4375 | 11.112 |
| 1/2 | 0.5000 | 12.700 |
| 9/16 | 0.5625 | 14.287 |
| 5/8 | 0.6250 | 15.875 |
| 3/4 | 0.7500 | 19.050 |
| 7/8 | 0.8750 | 22.225 |
| 1 | 1.0000 | 25.400 |
G pipe thread dimensions (BSPP, ISO 228)
G is the ISO 228-1 parallel pipe thread (BSPP); it seals with a washer or gasket, not on the thread.
| Size | TPI | Major diameter (mm) | Tap drill (mm) | Minor min (mm) | Minor max (mm) |
|---|---|---|---|---|---|
| G1/16 | 28 | 7.723 | 6.80 | 6.561 | 6.843 |
| G1/8 | 28 | 9.728 | 8.80 | 8.566 | 8.848 |
| G1/4 | 19 | 13.157 | 11.80 | 11.445 | 11.890 |
| G3/8 | 19 | 16.662 | 15.25 | 14.950 | 15.395 |
| G1/2 | 14 | 20.955 | 19.00 | 18.631 | 19.172 |
| G5/8 | 14 | 22.911 | 21.00 | 20.587 | 21.128 |
| G3/4 | 14 | 26.441 | 24.50 | 24.117 | 24.658 |
| G7/8 | 14 | 30.201 | 28.25 | 27.877 | 28.418 |
| G1 | 11 | 33.249 | 30.75 | 30.291 | 30.931 |
| G1-1/8 | 11 | 37.897 | 35.25 | 34.939 | 35.579 |
| G1-1/4 | 11 | 41.910 | 39.50 | 38.952 | 39.592 |
| G1-1/2 | 11 | 47.803 | 45.25 | 44.845 | 45.485 |
| G1-3/4 | 11 | 53.746 | 51.25 | 50.788 | 51.428 |
| G2 | 11 | 59.614 | 57.00 | 56.656 | 57.296 |
R / Rc taper pipe thread drill chart (BSPT, ISO 7)
R (external) / Rc (internal) are ISO 7-1 taper pipe threads with a 1:16 taper, sealing on the thread. Drill sizes vary slightly by tap maker (e.g. Rc1/8: 8.1–8.2 mm); use your tap maker's value. Rp is the parallel internal thread that mates with an R external thread; diameter tolerance per ISO 7-1.
| Size | TPI | Gauge diameter (mm) | Drill (tap-maker catalogs) (mm) |
|---|---|---|---|
| R/Rc 1/16 | 28 | 7.723 | 6.1 – 6.2 |
| R/Rc 1/8 | 28 | 9.728 | 8.1 – 8.2 |
| R/Rc 1/4 | 19 | 13.157 | 10.7 – 11.0 |
| R/Rc 3/8 | 19 | 16.662 | 14.2 – 14.5 |
| R/Rc 1/2 | 14 | 20.955 | 17.6 – 18.0 |
| R/Rc 3/4 | 14 | 26.441 | 23.0 – 23.5 |
| R/Rc 1 | 11 | 33.249 | 29.0 – 29.5 |
| R/Rc 1-1/4 | 11 | 41.910 | 37.5 – 38.0 |
| R/Rc 1-1/2 | 11 | 47.803 | 43.4 – 44.0 |
| R/Rc 2 | 11 | 59.614 | 54.9 – 55.5 |
Rp parallel pipe thread dimensions (ISO 7-1)
| Size | TPI | Tap drill (mm) | Minor min (mm) | Minor max (mm) |
|---|---|---|---|---|
| Rp 1/16 | 28 | 6.5 | 6.490 | 6.632 |
| Rp 1/8 | 28 | 8.5 | 8.495 | 8.637 |
| Rp 1/4 | 19 | 11.4 | 11.341 | 11.549 |
| Rp 3/8 | 19 | 14.9 | 14.846 | 15.054 |
| Rp 1/2 | 14 | 18.6 | 18.489 | 18.773 |
| Rp 3/4 | 14 | 24.1 | 23.975 | 24.259 |
| Rp 1 | 11 | 30.2 | 30.110 | 30.472 |
| Rp 1-1/4 | 11 | 38.9 | 38.771 | 39.133 |
| Rp 1-1/2 | 11 | 44.8 | 44.664 | 45.026 |
| Rp 2 | 11 | 56.6 | 56.475 | 56.837 |
NPT pipe thread drill chart
NPT is the American taper pipe thread (ASME B1.20.1), 60° angle, with two drill sizes: direct tapping, or a smaller drill followed by a taper reamer. NPS is the American straight pipe thread. Do not mix with R/Rc/G (55°). Drill sizes vary slightly by maker.
| Size | TPI | Tap drill | Tap drill (mm) | Drill with taper reamer | Drill with taper reamer (mm) |
|---|---|---|---|---|---|
| NPT 1/16-27 | 27 | D | 6.248 | 15/64 | 5.953 |
| NPT 1/8-27 | 27 | R | 8.611 | 21/64 | 8.334 |
| NPT 1/4-18 | 18 | 7/16 | 11.113 | 27/64 | 10.716 |
| NPT 3/8-18 | 18 | 37/64 | 14.684 | 9/16 | 14.288 |
| NPT 1/2-14 | 14 | 23/32 | 18.256 | 11/16 | 17.463 |
| NPT 3/4-14 | 14 | 59/64 | 23.416 | 57/64 | 22.622 |
| NPT 1-11.5 | 11.5 | 1-5/32 | 29.369 | 1-1/8 | 28.575 |
| NPT 1-1/4-11.5 | 11.5 | 1-1/2 | 38.100 | 1-15/32 | 37.306 |
| NPT 1-1/2-11.5 | 11.5 | 1-23/32 | 43.656 | 1-45/64 | 43.259 |
| NPT 2-11.5 | 11.5 | 2-3/16 | 55.563 | 2-11/64 | 55.166 |
NPS straight pipe thread drill chart
| Size | TPI | Tap drill | Tap drill (mm) |
|---|---|---|---|
| NPS 1/16-27 | 27 | 1/4 | 6.350 |
| NPS 1/8-27 | 27 | S | 8.839 |
| NPS 1/4-18 | 18 | 29/64 | 11.509 |
| NPS 3/8-18 | 18 | 19/32 | 15.081 |
| NPS 1/2-14 | 14 | 47/64 | 18.653 |
| NPS 3/4-14 | 14 | 15/16 | 23.813 |
| NPS 1-11.5 | 11.5 | 1-3/16 | 30.163 |
| NPS 1-1/4-11.5 | 11.5 | 1-33/64 | 38.497 |
| NPS 1-1/2-11.5 | 11.5 | 1-3/4 | 44.450 |
| NPS 2-11.5 | 11.5 | 2-7/32 | 56.356 |
Trapezoidal thread Tr dimensions (ISO 2904)
Metric trapezoidal thread per ISO 2904, 30° angle, used for lead screws, vises and presses.
| Size | P (mm) | d2 (mm) | d3 (mm) | D1 (mm) | D4 (mm) |
|---|---|---|---|---|---|
| Tr8 × 1.5 | 1.5 | 7.25 | 6.20 | 6.50 | 8.30 |
| Tr10 × 2 | 2.0 | 9.00 | 7.50 | 8.00 | 10.50 |
| Tr12 × 3 | 3.0 | 10.50 | 8.50 | 9.00 | 12.50 |
| Tr14 × 3 | 3.0 | 12.50 | 10.50 | 11.00 | 14.50 |
| Tr16 × 4 | 4.0 | 14.00 | 11.50 | 12.00 | 16.50 |
| Tr18 × 4 | 4.0 | 16.00 | 13.50 | 14.00 | 18.50 |
| Tr20 × 4 | 4.0 | 18.00 | 15.50 | 16.00 | 20.50 |
| Tr22 × 5 | 5.0 | 19.50 | 16.50 | 17.00 | 22.50 |
| Tr24 × 5 | 5.0 | 21.50 | 18.50 | 19.00 | 24.50 |
| Tr26 × 5 | 5.0 | 23.50 | 20.50 | 21.00 | 26.50 |
| Tr28 × 5 | 5.0 | 25.50 | 22.50 | 23.00 | 28.50 |
| Tr30 × 6 | 6.0 | 27.00 | 23.00 | 24.00 | 31.00 |
| Tr32 × 6 | 6.0 | 29.00 | 25.00 | 26.00 | 33.00 |
| Tr36 × 6 | 6.0 | 33.00 | 29.00 | 30.00 | 37.00 |
| Tr40 × 7 | 7.0 | 36.50 | 32.00 | 33.00 | 41.00 |
| Tr44 × 7 | 7.0 | 40.50 | 36.00 | 37.00 | 45.00 |
| Tr50 × 8 | 8.0 | 46.00 | 41.00 | 42.00 | 51.00 |
Helicoil insert drill chart (STI taps)
Wire thread inserts (Helicoil) need a larger hole and a dedicated STI tap, not the normal tap drill. Values follow Heli-Coil drilling data; check the catalog for other sizes or brands.
| Size | Drill – aluminum (mm) | Drill – steel, magnesium, plastic (mm) | Drilled hole (min – max) | STI tap |
|---|---|---|---|---|
| M3 × 0.5 | 3.15 | 3.20 | 3.108 – 3.220 | M3 × 0.5 STI |
| M4 × 0.7 | 4.20 | 4.25 | 4.152 – 4.292 | M4 × 0.7 STI |
| M5 × 0.8 | 5.20 | 5.30 | 5.174 – 5.334 | M5 × 0.8 STI |
| M6 × 1 | 6.25 | 6.30 | 6.217 – 6.407 | M6 × 1 STI |
| M8 × 1.25 | 8.30 | 8.40 | 8.271 – 8.483 | M8 × 1.25 STI |
| M10 × 1.5 | 10.50 | 10.50 | 10.324 – 10.560 | M10 × 1.5 STI |
| M12 × 1.75 | 12.50 | 12.50 | 12.379 – 12.644 | M12 × 1.75 STI |
| M14 × 2 | 14.50 | 14.50 | 14.433 – 14.733 | M14 × 2 STI |
| M16 × 2 | 16.50 | 16.50 | 16.433 – 16.733 | M16 × 2 STI |
| M18 × 2.5 | 18.75 | 18.75 | — | M18 × 2.5 STI |
| M20 × 2.5 | 20.75 | 20.75 | 20.541 – 20.896 | M20 × 2.5 STI |
| M22 × 2.5 | 22.75 | 22.75 | — | M22 × 2.5 STI |
| M24 × 3 | 24.75 | 24.75 | — | M24 × 3 STI |
| M8 × 1 | 8.25 | 8.30 | 8.217 – 8.407 | M8 × 1 STI |
| M10 × 1 | 10.25 | 10.25 | 10.217 – 10.407 | M10 × 1 STI |
| M10 × 1.25 | 10.25 | 10.25 | 10.271 – 10.483 | M10 × 1.25 STI |
| M12 × 1.25 | 12.25 | 12.25 | 12.271 – 12.483 | M12 × 1.25 STI |
| M12 × 1.5 | 12.25 | 12.50 | 12.324 – 12.560 | M12 × 1.5 STI |
| M14 × 1.5 | 14.25 | 14.50 | 14.324 – 14.560 | M14 × 1.5 STI |
| M16 × 1.5 | 16.25 | 16.50 | 16.324 – 16.560 | M16 × 1.5 STI |
| M18 × 1.5 | 18.25 | 18.50 | — | M18 × 1.5 STI |
| M18 × 2 | 18.50 | 18.50 | — | M18 × 2 STI |
| M20 × 1.5 | 20.25 | 20.50 | 20.324 – 20.560 | M20 × 1.5 STI |
| M20 × 2 | 20.50 | 20.50 | 20.433 – 20.733 | M20 × 2 STI |
| M22 × 1.5 | 22.25 | 22.50 | — | M22 × 1.5 STI |
Reference tapping speeds (m/min)
Vc values are starting points for coated HSS-E taps with cutting oil; forming taps can run about 20% faster (not on cast iron). Blind-hole drill depth = thread depth + 3 pitches (tap chamfer) + 0.3 × drill diameter (118° point). For rigid tapping, F = S × P.
| Material | Cutting tap (coated HSS-E) | Forming tap |
|---|---|---|
| Low-carbon steel (SS400, 1020) | 10 – 15 | 12 – 18 |
| Medium-carbon & alloy steel (1045, 4140) | 6 – 10 | 7 – 12 |
| Stainless (304, 316) | 4 – 8 | 5 – 10 |
| Grey cast iron (FC200, FC250) | 10 – 15 | — |
| Aluminum alloy (6061, 7075) | 20 – 30 | 24 – 36 |
| Brass (C3604) | 15 – 25 | 18 – 30 |