Free tap drill chart for NC, NF, Metric Coarse & Fine threads. Includes inch, mm, decimal sizes, SVG diagram, formula & FAQ. Print-ready reference for machinists.
Reference for NC, NF, Metric Coarse & Fine threads (75% thread engagement)
Formula: Tap Drill = Major Ø − (1.299 × Pitch × %Thread / 100)
| Tap Size | TPI | Drill Size | Decimal (in) | mm |
|---|---|---|---|---|
| #1-64 | 64 | #53 | 0.0595 | 1.51 |
| #2-56 | 56 | #50 | 0.0700 | 1.78 |
| #3-48 | 48 | #47 | 0.0785 | 1.99 |
| #4-40 | 40 | #43 | 0.0890 | 2.26 |
| #5-40 | 40 | #38 | 0.1015 | 2.58 |
| #6-32 | 32 | #36 | 0.1065 | 2.71 |
| #8-32 | 32 | #29 | 0.1360 | 3.45 |
| #10-24 | 24 | #25 | 0.1495 | 3.80 |
| #12-24 | 24 | #16 | 0.1770 | 4.50 |
| 1/4-20 | 20 | #7 | 0.2010 | 5.11 |
| 5/16-18 | 18 | F | 0.2570 | 6.53 |
| 3/8-16 | 16 | 5/16 | 0.3125 | 7.94 |
| 7/16-14 | 14 | U | 0.3680 | 9.35 |
| 1/2-13 | 13 | 27/64 | 0.4219 | 10.72 |
| 9/16-12 | 12 | 31/64 | 0.4844 | 12.30 |
| 5/8-11 | 11 | 17/32 | 0.5312 | 13.49 |
| 3/4-10 | 10 | 21/32 | 0.6562 | 16.67 |
| 7/8-9 | 9 | 49/64 | 0.7656 | 19.45 |
| 1"-8 | 8 | 7/8 | 0.8750 | 22.23 |
| 1-1/8"-7 | 7 | 63/64 | 0.9844 | 25.00 |
| 1-1/4"-7 | 7 | 1-7/64 | 1.1094 | 28.18 |
| 1-1/2"-6 | 6 | 1-11/32 | 1.3437 | 34.13 |
| Tap Size | TPI | Drill Size | Decimal (in) | mm |
|---|---|---|---|---|
| #0-80 | 80 | 3/64 | 0.0469 | 1.19 |
| #1-72 | 72 | #53 | 0.0595 | 1.51 |
| #2-64 | 64 | #50 | 0.0700 | 1.78 |
| #3-56 | 56 | #45 | 0.0820 | 2.08 |
| #4-48 | 48 | #42 | 0.0935 | 2.37 |
| #5-44 | 44 | #37 | 0.1040 | 2.64 |
| #6-40 | 40 | #33 | 0.1130 | 2.87 |
| #8-36 | 36 | #29 | 0.1360 | 3.45 |
| #10-32 | 32 | #21 | 0.1590 | 4.04 |
| #12-28 | 28 | #14 | 0.1820 | 4.62 |
| 1/4-28 | 28 | #3 | 0.2130 | 5.41 |
| 5/16-24 | 24 | I | 0.2720 | 6.91 |
| 3/8-24 | 24 | Q | 0.3320 | 8.43 |
| 7/16-20 | 20 | 25/64 | 0.3906 | 9.92 |
| 1/2-20 | 20 | 29/64 | 0.4531 | 11.51 |
| 9/16-18 | 18 | 33/64 | 0.5156 | 13.10 |
| 5/8-18 | 18 | 37/64 | 0.5781 | 14.68 |
| 3/4-16 | 16 | 11/16 | 0.6875 | 17.46 |
| 7/8-14 | 14 | 13/16 | 0.8125 | 20.64 |
| 1"-14 | 14 | 15/16 | 0.9375 | 23.81 |
| 1-1/8"-12 | 12 | 1-3/64 | 1.0469 | 26.59 |
| 1-1/4"-12 | 12 | 1-11/64 | 1.1719 | 29.77 |
| 1-1/2"-12 | 12 | 1-27/64 | 1.4219 | 36.12 |
| Tap Size | Pitch (mm) | Drill (mm) | Drill (in) | Closest Inch |
|---|---|---|---|---|
| M1.6 | 0.35 | 1.25 | 0.0492 | #55 |
| M2 | 0.40 | 1.60 | 0.0630 | #52 |
| M2.5 | 0.45 | 2.05 | 0.0807 | #46 |
| M3 | 0.50 | 2.50 | 0.0984 | #39 |
| M3.5 | 0.60 | 2.90 | 0.1142 | #33 |
| M4 | 0.70 | 3.30 | 0.1299 | #30 |
| M5 | 0.80 | 4.20 | 0.1654 | #19 |
| M6 | 1.00 | 5.00 | 0.1969 | #9 |
| M7 | 1.00 | 6.00 | 0.2362 | B |
| M8 | 1.25 | 6.80 | 0.2677 | H |
| M10 | 1.50 | 8.50 | 0.3346 | R |
| M12 | 1.75 | 10.20 | 0.4016 | Y |
| M14 | 2.00 | 12.00 | 0.4724 | 15/32 |
| M16 | 2.00 | 14.00 | 0.5512 | 35/64 |
| M18 | 2.50 | 15.50 | 0.6102 | 39/64 |
| M20 | 2.50 | 17.50 | 0.6890 | 11/16 |
| M22 | 2.50 | 19.50 | 0.7677 | 49/64 |
| M24 | 3.00 | 21.00 | 0.8268 | 53/64 |
| M27 | 3.00 | 24.00 | 0.9449 | 15/16 |
| M30 | 3.50 | 26.50 | 1.0433 | 1-3/64 |
| Tap Size | Pitch (mm) | Drill (mm) | Drill (in) | Closest Inch |
|---|---|---|---|---|
| M3 × 0.35 | 0.35 | 2.65 | 0.1043 | #37 |
| M4 × 0.5 | 0.50 | 3.50 | 0.1378 | #28 |
| M5 × 0.5 | 0.50 | 4.50 | 0.1772 | #16 |
| M6 × 0.75 | 0.75 | 5.25 | 0.2067 | #5 |
| M8 × 1.0 | 1.00 | 7.00 | 0.2756 | J |
| M10 × 1.0 | 1.00 | 9.00 | 0.3543 | T |
| M10 × 1.25 | 1.25 | 8.80 | 0.3465 | S |
| M12 × 1.25 | 1.25 | 10.80 | 0.4252 | 27/64 |
| M12 × 1.5 | 1.50 | 10.50 | 0.4134 | Z |
| M14 × 1.5 | 1.50 | 12.50 | 0.4921 | 31/64 |
| M16 × 1.5 | 1.50 | 14.50 | 0.5709 | 37/64 |
| M18 × 1.5 | 1.50 | 16.50 | 0.6496 | 41/64 |
| M20 × 1.5 | 1.50 | 18.50 | 0.7283 | 47/64 |
| M22 × 1.5 | 1.50 | 20.50 | 0.8071 | 51/64 |
| M24 × 2.0 | 2.00 | 22.00 | 0.8661 | 55/64 |
| M27 × 2.0 | 2.00 | 25.00 | 0.9843 | 63/64 |
| M30 × 2.0 | 2.00 | 28.00 | 1.1024 | 1-7/64 |
1. What is a tap drill?
A tap drill is the bit used to drill a hole before threading it with a tap. Its diameter must be smaller than the screw's major diameter so the tap can cut threads into the wall of the hole. Using the wrong size produces weak threads (too big) or breaks the tap (too small).
2. How do I calculate tap drill size?
Use the formula:
Tap Drill Ø = Major Ø − (1.299 × Pitch × %Thread / 100)
For imperial threads, Pitch = 1 / TPI. Industry standard uses 75% thread engagement, which balances strength and ease of tapping.
3. Why is 75% thread engagement standard?
Tests show 75% thread holds ~95% of the strength of a 100% thread, but takes only 1/3 of the tapping torque. This dramatically reduces broken taps and is the recommended engagement for most general machining work.
4. What's the difference between NC and NF?
NC (National Coarse / UNC) has fewer threads per inch — stronger in soft materials, faster to assemble, more forgiving of damage.
NF (National Fine / UNF) has more threads per inch — better for thin-wall parts, fine adjustment, and high vibration resistance.
5. Can I use an imperial drill bit for a metric tap?
Yes — every metric size in the chart shows the closest imperial fraction or letter/number drill. Match the decimal as closely as possible. Going slightly larger (within 0.05 mm) reduces tap breakage; going smaller increases thread strength but raises torque.
6. Why did my tap break?
The 5 most common causes:
① Tap drill too small (over-engagement)
② Not backing off to clear chips every 1–2 turns
③ No cutting fluid
④ Tap not aligned square to the hole
⑤ Wrong tap type (taper / plug / bottoming) for blind holes
7. What cutting fluid should I use for tapping?
Steel: sulfur-based or chlorinated tapping oil.
Aluminum: kerosene, WD-40, or aluminum-specific tap fluid.
Stainless: heavy sulfur-chlorinated paste.
Cast iron: tap dry or with light air blast.
Brass / bronze: tap dry, or light oil.
8. How deep should a tapped hole be?
As a rule of thumb:
• Steel into steel: 1 × diameter of thread engagement
• Steel into aluminum / brass: 2 × diameter
• Steel into plastic: 2.5–3 × diameter
For blind holes, drill at least 3–4 extra pitches deeper than the tap will travel, to allow chip clearance.
Questions about your project? Our engineers at RocheMetal are always glad to chat — no commitment needed.