Choosing the wrong tap drill costs you a broken tap, a stripped hole, or a scrapped part. This guide gives you the exact drill size for standard (UNC/UNF), metric, and pipe threads — at both 75% and 50% thread engagement — so you get it right the first time.
You'll get:
Use the 75% thread drill for aluminum, brass, and plastics, and the 50% thread drill for steel, stainless, and iron. Clearance drills are for through-holes the screw passes through.
| Thread | TPI | Tap drill 75% (Al, brass, plastic) |
Tap drill 50% (steel, stainless) |
Clearance close fit |
Clearance free fit |
|---|---|---|---|---|---|
| #4-40 | 40 | #43 (.089) | #41 (.096) | #32 (.116) | #30 (.129) |
| #6-32 | 32 | #36 (.107) | #32 (.116) | #27 (.144) | #25 (.150) |
| #8-32 | 32 | #29 (.136) | #27 (.144) | #18 (.170) | #16 (.177) |
| #10-24 | 24 | #22 (.157) | #20 (.161) | #9 (.196) | #7 (.201) |
| #10-32 | 32 | #21 (.159) | #18 (.170) | #9 (.196) | #7 (.201) |
| 1/4"-20 | 20 | #7 (.201) | 7/32" (.219) | F (.257) | H (.266) |
| 1/4"-28 | 28 | #3 (.213) | #1 (.228) | F (.257) | H (.266) |
| 5/16"-18 | 18 | F (.257) | J (.277) | P (.323) | Q (.332) |
| 5/16"-24 | 24 | I (.272) | 9/32" (.281) | P (.323) | Q (.332) |
| 3/8"-16 | 16 | 5/16" (.313) | Q (.332) | W (.386) | X (.397) |
| 3/8"-24 | 24 | Q (.332) | S (.348) | W (.386) | X (.397) |
| 7/16"-14 | 14 | U (.368) | 25/64" (.391) | 29/64" (.453) | 15/32" (.469) |
| 1/2"-13 | 13 | 27/64" (.422) | 29/64" (.453) | 33/64" (.516) | 17/32" (.531) |
| 1/2"-20 | 20 | 29/64" (.453) | 15/32" (.469) | 33/64" (.516) | 17/32" (.531) |
| 5/8"-11 | 11 | 17/32" (.531) | 9/16" (.563) | 41/64" (.641) | 21/32" (.656) |
| 3/4"-10 | 10 | 21/32" (.656) | 11/16" (.688) | 49/64" (.766) | 25/32" (.781) |
Drill sizes for coarse-pitch metric threads. The pitch drives the drill size — always match both (e.g. M8×1.25).
| Thread × pitch | Tap drill 75% (mm) | Tap drill 50% (mm) |
|---|---|---|
| M3 × 0.5 | 2.50 | 2.70 |
| M4 × 0.7 | 3.30 | 3.50 |
| M5 × 0.8 | 4.20 | 4.50 |
| M6 × 1.0 | 5.00 | 5.40 |
| M8 × 1.25 | 6.80 | 7.20 |
| M10 × 1.5 | 8.50 | 9.00 |
| M12 × 1.75 | 10.30 | 10.90 |
| M14 × 2.0 | 12.10 | 12.70 |
| M16 × 2.0 | 14.00 | 14.75 |
| M20 × 2.0 | 18.00 | 18.50 |
Tapered pipe threads (NPT / NPTF) seal by wedging; straight pipe threads (NPS) do not.
| Tap size | Drill — NPT / NPTF (taper) | Drill — NPS (straight) |
|---|---|---|
| 1/8"-27 | R (.339) | S (.348) |
| 1/4"-18 | 7/16" (.4375) | 29/64" (.4531) |
| 3/8"-18 | 37/64" (.5781) | 19/32" (.5938) |
| 1/2"-14 | 23/32" (.7188) | 47/64" (.7344) |
| 3/4"-14 | 59/64" (.9219) | 15/16" (.9375) |
| 1"-11.5 | 1-5/32" (1.1562) | 1-3/16" (1.1875) |
| 1-1/4"-11.5 | 1-1/2" (1.5000) | 1-33/64" (1.5156) |
| 1-1/2"-11.5 | 1-47/64" (1.7344) | 1-3/4" (1.7500) |
| 2"-11.5 | 2-7/32" (2.2188) | 2-7/32" (2.2188) |
Download the complete Tap & Drill Chart PDF — all standard, metric, plug tap and pipe sizes.
A tap drill chart tells you the hole size to drill before cutting internal threads with a tap. Pick the right size and the thread is strong and the tap runs freely; too small and you spike tapping torque and risk snapping the tap; too large and the threads lose holding strength.
Most shop work targets about a 75% thread — the best balance of strength and ease of tapping. In tougher materials like steel and stainless, dropping to roughly 50% thread (a slightly larger drill) cuts tapping torque and tap breakage with little loss of holding power.
The major diameter is the distance across the outer crests of the thread; the minor diameter is across the inner roots. The tap drill produces a hole close to the minor diameter so the tap can cut clean threads.
No. A tap cuts internal threads and needs a drilled hole first. A die cuts external threads onto a rod or bolt and needs no drill — so a "tap and die drill chart" really only applies to the tapping side.
Use a #7 drill (0.201") for a 1/4"-20 UNC thread at 75% thread engagement.
What drill size is used for an M8 tap?An M8×1.25 thread uses a 6.8 mm drill. For the fine-pitch M8×1.0, use 7.0 mm.
What thread engagement should a tap drill give?About 75% for general work; roughly 50% in steel and stainless to lower tapping torque.
Do I need a drill size for a die?No. Dies cut external threads and need no drilled hole — only taps require a tap drill.