Guide · Thread technology
Tap drill size chart (metric)
Every metric coarse thread needs a hole before it is cut, and the size follows one rule: tap drill = nominal diameter minus pitch. The chart below gives the tap drill and the clearance hole for M3 to M16, so you can pick the drill and the matching screw in one go.
Chart
Tap drill sizes M3–M16
| Thread | Pitch (mm) | Tap drill (mm) | Clearance hole (mm) |
|---|---|---|---|
| M3 | 0.50 | 2.5 | 3.4 |
| M4 | 0.70 | 3.3 | 4.5 |
| M5 | 0.80 | 4.2 | 5.5 |
| M6 | 1.00 | 5.0 | 6.6 |
| M8 | 1.25 | 6.8 | 9.0 |
| M10 | 1.50 | 8.5 | 11.0 |
| M12 | 1.75 | 10.2 | 13.5 |
| M16 | 2.00 | 14.0 | 17.5 |
Values for metric ISO coarse thread (DIN 13); clearance hole in the “medium” series to ISO 273 (formerly DIN EN 20273). Fine threads have different pitches and therefore different tap drill sizes.
Read the row for your thread, then decide which column applies. The tap drill column is the hole you drill before cutting an internal thread. The clearance hole column is the larger hole in the part the screw passes through. Both are metric throughout — no conversion, no fractional drill sizes.
Rule of thumb
How the tap drill size is calculated
For a metric coarse thread, the drill for the tap drill hole (internal thread, thread cutting) is approximately the nominal diameter minus the thread pitch. Example M8 (pitch 1.25 mm): 8 − 1.25 = 6.75 → a 6.8 mm drill. The same arithmetic gives M6 (pitch 1.0 mm): 6 − 1 = 5.0 mm. For a clearance hole — where the screw is only pushed through — the values follow ISO 273 (formerly DIN EN 20273) instead, and they are listed in the chart above.
The formula is an approximation, which is why the chart rounds to the nearest standard drill size. Where a table value and your own calculation differ by 0.1 mm, take the table value.
FAQ
Frequently asked questions
What drill size do I need for an M8 thread?
For the tap drill hole (cutting an internal thread), a 6.8 mm drill. If the M8 screw is only pushed through, drill a clearance hole of 9.0 mm (medium series).
How do I calculate the tap drill size?
Approximately: nominal diameter minus thread pitch. Example M6 (pitch 1.0 mm): 6 − 1 = 5.0 mm.
What is the difference between a tap drill hole and a clearance hole?
The tap drill hole is drilled so that a thread can be cut into it afterwards. The larger clearance hole lets the screw pass through without a thread.
Do these values apply to fine threads as well?
No. Fine threads (for example M8×1) have a smaller pitch and therefore a larger tap drill hole — separate charts apply to them.
Related
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