Reference & Charts
Thread, Drill & Tap Reference
A searchable thread, drill, and tap tool covering both systems in one place: Unified inch (UNC/UNF) and metric (coarse and fine). Look up thread pitch or TPI, major diameter, the tap drill for a ~75% thread, and a clearance-hole size where a reliable standard exists. Search by size (e.g. 1/4, M6) or filter by system and series.
43 entries · Last verified: 2026-07-17
Two threading systems, one lookup. Search by size (type “1/4” or “M6”) or filter by system and series to find the tap drill for a ~75% thread — the common shop default that balances thread strength against tapping torque and the risk of breaking a tap. Inch tap drills are given as the standard number, letter, or fraction with the decimal diameter; metric as the drill diameter in millimetres.
Tap-drill sizes are the widely-used ~75% values, not the only correct choice: a larger drill produces a lower thread percentage (easier tapping, slightly weaker thread) and a smaller drill a higher percentage (stronger but harder to tap). For hard or gummy materials, or hand tapping, dropping to ~65–70% is common. Verify critical joints against your own standard.
Showing 43 of 43
| Thread | System | Series | Pitch / TPI | Major Ø | Tap drill (~75%) | Clearance hole |
|---|---|---|---|---|---|---|
| #4-40 | Inch | Coarse (UNC) | 40 TPI | 0.112" | #43 (0.089") | — |
| #6-32 | Inch | Coarse (UNC) | 32 TPI | 0.138" | #36 (0.1065") | — |
| #8-32 | Inch | Coarse (UNC) | 32 TPI | 0.164" | #29 (0.136") | — |
| #10-24 | Inch | Coarse (UNC) | 24 TPI | 0.19" | #25 (0.1495") | — |
| #12-24 | Inch | Coarse (UNC) | 24 TPI | 0.216" | #16 (0.177") | — |
| 1/4"-20 | Inch | Coarse (UNC) | 20 TPI | 0.25" | #7 (0.201") | 17/64" (0.266") |
| 5/16"-18 | Inch | Coarse (UNC) | 18 TPI | 0.3125" | F (0.257") | 21/64" (0.328") |
| 3/8"-16 | Inch | Coarse (UNC) | 16 TPI | 0.375" | 5/16" (0.3125") | 25/64" (0.391") |
| 7/16"-14 | Inch | Coarse (UNC) | 14 TPI | 0.4375" | U (0.368") | 29/64" (0.453") |
| 1/2"-13 | Inch | Coarse (UNC) | 13 TPI | 0.5" | 27/64" (0.4219") | 33/64" (0.516") |
| 9/16"-12 | Inch | Coarse (UNC) | 12 TPI | 0.5625" | 31/64" (0.4844") | 37/64" (0.578") |
| 5/8"-11 | Inch | Coarse (UNC) | 11 TPI | 0.625" | 17/32" (0.5312") | 41/64" (0.641") |
| 3/4"-10 | Inch | Coarse (UNC) | 10 TPI | 0.75" | 21/32" (0.6562") | 49/64" (0.766") |
| #4-48 | Inch | Fine (UNF) | 48 TPI | 0.112" | #42 (0.0935") | — |
| #6-40 | Inch | Fine (UNF) | 40 TPI | 0.138" | #33 (0.113") | — |
| #8-36 | Inch | Fine (UNF) | 36 TPI | 0.164" | #29 (0.136") | — |
| #10-32 | Inch | Fine (UNF) | 32 TPI | 0.19" | #21 (0.159") | — |
| 1/4"-28 | Inch | Fine (UNF) | 28 TPI | 0.25" | #3 (0.213") | 17/64" (0.266") |
| 5/16"-24 | Inch | Fine (UNF) | 24 TPI | 0.3125" | I (0.272") | 21/64" (0.328") |
| 3/8"-24 | Inch | Fine (UNF) | 24 TPI | 0.375" | Q (0.332") | 25/64" (0.391") |
| 7/16"-20 | Inch | Fine (UNF) | 20 TPI | 0.4375" | 25/64" (0.3906") | 29/64" (0.453") |
| 1/2"-20 | Inch | Fine (UNF) | 20 TPI | 0.5" | 29/64" (0.4531") | 33/64" (0.516") |
| 9/16"-18 | Inch | Fine (UNF) | 18 TPI | 0.5625" | 33/64" (0.5156") | 37/64" (0.578") |
| 5/8"-18 | Inch | Fine (UNF) | 18 TPI | 0.625" | 37/64" (0.5781") | 41/64" (0.641") |
| 3/4"-16 | Inch | Fine (UNF) | 16 TPI | 0.75" | 11/16" (0.6875") | 49/64" (0.766") |
| M2 × 0.4 | Metric | Coarse | 0.40 mm | 2.00 mm | 1.6 mm | 2.4 mm |
| M2.5 × 0.45 | Metric | Coarse | 0.45 mm | 2.50 mm | 2.05 mm | 2.9 mm |
| M3 × 0.5 | Metric | Coarse | 0.50 mm | 3.00 mm | 2.5 mm | 3.4 mm |
| M4 × 0.7 | Metric | Coarse | 0.70 mm | 4.00 mm | 3.3 mm | 4.5 mm |
| M5 × 0.8 | Metric | Coarse | 0.80 mm | 5.00 mm | 4.2 mm | 5.5 mm |
| M6 × 1.0 | Metric | Coarse | 1.00 mm | 6.00 mm | 5 mm | 6.6 mm |
| M8 × 1.25 | Metric | Coarse | 1.25 mm | 8.00 mm | 6.8 mm | 9 mm |
| M10 × 1.5 | Metric | Coarse | 1.50 mm | 10.00 mm | 8.5 mm | 11 mm |
| M12 × 1.75 | Metric | Coarse | 1.75 mm | 12.00 mm | 10.2 mm | 13.5 mm |
| M16 × 2.0 | Metric | Coarse | 2.00 mm | 16.00 mm | 14 mm | 17.5 mm |
| M20 × 2.5 | Metric | Coarse | 2.50 mm | 20.00 mm | 17.5 mm | 22 mm |
| M8 × 1.0 | Metric | Fine | 1.00 mm | 8.00 mm | 7 mm | 9 mm |
| M10 × 1.25 | Metric | Fine | 1.25 mm | 10.00 mm | 8.75 mm | 11 mm |
| M10 × 1.0 | Metric | Fine | 1.00 mm | 10.00 mm | 9 mm | 11 mm |
| M12 × 1.5 | Metric | Fine | 1.50 mm | 12.00 mm | 10.5 mm | 13.5 mm |
| M12 × 1.25 | Metric | Fine | 1.25 mm | 12.00 mm | 10.75 mm | 13.5 mm |
| M16 × 1.5 | Metric | Fine | 1.50 mm | 16.00 mm | 14.5 mm | 17.5 mm |
| M20 × 1.5 | Metric | Fine | 1.50 mm | 20.00 mm | 18.5 mm | 22 mm |
Select a thread for its full spec sheet.
Frequently asked
- Do the tap drills work for both inch and metric here?
- Yes — each row lists the tap drill in its own system. Inch threads (UNC/UNF) show the standard number/letter/fraction drill and its decimal size (ASME B1.1); metric threads show the drill diameter in millimetres. All are for a ~75% thread.
- How is the metric tap drill calculated?
- By the shop rule for a ~75% thread: tap drill = major diameter − pitch. An M6 × 1.0 taps with a 5.0 mm drill (6 − 1.0); an M8 × 1.0 fine thread taps with 7.0 mm. It's an approximation that matches the standard drills used in practice.
- Why is the clearance hole blank for some inch sizes?
- Clearance is shown where a single reliable standard value applies: metric uses the ISO 273 normal fit, and inch fractional sizes use the close fit (nominal + 1/64"). Inch machine-screw (number) sizes and other fit classes (normal/loose) depend on the fit you want — use the Clearance Hole Calculator for those.
- What's the difference between the tap drill and the clearance hole?
- The tap drill is the smaller hole you cut the thread into (the female side). The clearance hole is the larger hole the bolt passes through (the male side). For M6: tap with 5.0 mm, clear with 6.6 mm. Tapping a clearance-sized hole leaves almost no thread.
Sources
- ASME B1.1 — Unified Inch Screw Threads (UNC/UNF): TPI and major diameter
- ISO 261 / ISO 262 — ISO general-purpose metric screw threads (coarse and fine pitch)
- ISO 273 — clearance holes for bolts and screws (normal fit, metric)
- Standard machinist tap-drill sizing for ~75% thread engagement