Tap Drill Diameter — ISO Metric Thread
This table covers both coarse and fine ISO metric threads for a quick tap-drill lookup. Match both the nominal thread size and the pitch shown on the drawing.
Rule of thumb: tap drill Ø ≈ nominal Ø − pitch. Use the “Tap drill” column for the standard value.
Coarse pitch (並目)| Thread | Pitch (mm) | Tap drill (mm) | Minor Ø min (mm) | Minor Ø max (mm) |
|---|
| M1×0.25 | 0.25 | 0.75 | 0.729 | 0.785 |
| M1.1×0.25 | 0.25 | 0.85 | 0.829 | 0.885 |
| M1.2×0.25 | 0.25 | 0.95 | 0.929 | 0.985 |
| M1.4×0.3 | 0.30 | 1.10 | 1.075 | 1.142 |
| M1.6×0.35 | 0.35 | 1.25 | 1.221 | 1.321 |
| M1.8×0.35 | 0.35 | 1.45 | 1.421 | 1.521 |
| M2×0.4 | 0.40 | 1.60 | 1.567 | 1.679 |
| M2.2×0.45 | 0.45 | 1.75 | 1.713 | 1.838 |
| M2.5×0.45 | 0.45 | 2.05 | 2.013 | 2.138 |
| M3×0.5 | 0.50 | 2.50 | 2.459 | 2.599 |
| M3.5×0.6 | 0.60 | 2.90 | 2.850 | 3.010 |
| M4×0.7 | 0.70 | 3.30 | 3.242 | 3.422 |
| M4.5×0.75 | 0.75 | 3.70 | 3.688 | 3.878 |
| M5×0.8 | 0.80 | 4.20 | 4.134 | 4.334 |
| M6×1 | 1.00 | 5.00 | 4.917 | 5.153 |
| M7×1 | 1.00 | 6.00 | 5.917 | 6.153 |
| M8×1.25 | 1.25 | 6.80 | 6.647 | 6.912 |
| M9×1.25 | 1.25 | 7.80 | 7.647 | 7.912 |
| M10×1.5 | 1.50 | 8.50 | 8.376 | 8.676 |
| M11×1.5 | 1.50 | 9.50 | 9.376 | 9.676 |
| M12×1.75 | 1.75 | 10.20 | 10.106 | 10.441 |
| M14×2 | 2.00 | 12.00 | 11.835 | 12.210 |
| M16×2 | 2.00 | 14.00 | 13.835 | 14.210 |
| M18×2.5 | 2.50 | 15.50 | 15.294 | 15.744 |
| M20×2.5 | 2.50 | 17.50 | 17.294 | 17.744 |
| M22×2.5 | 2.50 | 19.50 | 19.294 | 19.744 |
| M24×3 | 3.00 | 21.00 | 20.752 | 21.252 |
| M27×3 | 3.00 | 24.00 | 23.752 | 24.252 |
| M30×3.5 | 3.50 | 26.50 | 26.211 | 26.771 |
| M33×3.5 | 3.50 | 29.50 | 29.211 | 29.771 |
| M36×4 | 4.00 | 32.00 | 31.670 | 32.270 |
| M39×4 | 4.00 | 35.00 | 34.670 | 35.270 |
| M42×4.5 | 4.50 | 37.50 | 37.129 | 37.799 |
| M45×4.5 | 4.50 | 40.50 | 40.129 | 40.799 |
| M48×5 | 5.00 | 43.00 | 42.587 | 43.297 |
| M52×5 | 5.00 | 47.00 | 46.587 | 47.297 |
| M56×5.5 | 5.50 | 50.50 | 50.046 | 50.796 |
Fine pitch (細目)| Thread | Pitch (mm) | Tap drill (mm) |
|---|
| M6×0.75 | 0.75 | 5.25 |
| M8×1 | 1.00 | 7.00 |
| M8×0.75 | 0.75 | 7.25 |
| M10×1.25 | 1.25 | 8.75 |
| M10×1 | 1.00 | 9.00 |
| M12×1.5 | 1.50 | 10.50 |
| M12×1.25 | 1.25 | 10.75 |
| M12×1 | 1.00 | 11.00 |
| M14×1.5 | 1.50 | 12.50 |
| M16×1.5 | 1.50 | 14.50 |
| M18×2 | 2.00 | 16.00 |
| M18×1.5 | 1.50 | 16.50 |
| M20×2 | 2.00 | 18.00 |
| M20×1.5 | 1.50 | 18.50 |
| M22×1.5 | 1.50 | 20.50 |
| M24×2 | 2.00 | 22.00 |
| M24×1.5 | 1.50 | 22.50 |
| M27×2 | 2.00 | 25.00 |
| M30×2 | 2.00 | 28.00 |
| M33×2 | 2.00 | 31.00 |
| M36×3 | 3.00 | 33.00 |
| M36×2 | 2.00 | 34.00 |
| M39×3 | 3.00 | 36.00 |
| M42×3 | 3.00 | 39.00 |
| M45×3 | 3.00 | 42.00 |
| M48×3 | 3.00 | 45.00 |
“Tap drill” = recommended drill diameter before cutting a standard thread. “Minor Ø min/max” = internal-thread minor-diameter limits of the tapped hole (6H tolerance per ISO 965), for gauge checking. Form (roll) tapping needs a larger pilot hole — see a separate table.
Frequently asked questions
What tap drill is used for an M6 × 1 thread?
The M6 × 1 row in this table gives a 5.00 mm tap-drill diameter.
Can I select the drill from nominal diameter alone?
No. One nominal diameter can have several pitches, so both thread size and pitch must match the drawing.
Does this table apply to form tapping?
No. These tap-drill values are for conventional cutting taps. Form taps require a larger pilot hole from the tool maker's dedicated table.
MINATA — minatavn.com