Metric tap drill chart
For ISO metric coarse threads the tap drill is close to major diameter minus pitch: M6 × 1 takes a 5.0 mm drill. The chart below gives every standard size with the % thread it cuts.
| Thread | Tap drill | in | mm | Thread |
|---|---|---|---|---|
| M2 × 0.4 | 1.6 mm | 0.0630 | 1.60 | 77% |
| M2.5 × 0.45 | 2.05 mm | 0.0807 | 2.05 | 77% |
| M3 × 0.5 | 2.5 mm | 0.0984 | 2.50 | 77% |
| M4 × 0.7 | 3.3 mm | 0.1299 | 3.30 | 77% |
| M5 × 0.8 | 4.2 mm | 0.1654 | 4.20 | 77% |
| M6 × 1 | 5.0 mm | 0.1969 | 5.00 | 77% |
| M8 × 1.25 | 6.8 mm | 0.2677 | 6.80 | 74% |
| M10 × 1.5 | 8.5 mm | 0.3346 | 8.50 | 77% |
| M12 × 1.75 | 10.2 mm (or 10.3 mm) | 0.4016 | 10.20 | 79% |
| M16 × 2 | 14.0 mm | 0.5512 | 14.00 | 77% |
M12: charts split between 10.2 mm (about 79% thread) and 10.3 mm (about 75%). Both work; 10.3 mm is easier on the tap.
Calculator
Change the target engagement or check what an inch drill does to a metric thread. Inch sizes are on the inch tap drill chart.
75% is the chart standard. Go lower for stainless, hard steel or deep holes; it is easier on the tap and loses little strength.
| Set | Drill | in | mm | Thread |
|---|---|---|---|---|
| Fractional | 13/64" | 0.2031 | 5.16 | 65% |
| Number | #8 | 0.1990 | 5.05 | 73% |
| Letter | no letter drill fits this thread | |||
| Metric | 5.0 mm | 0.1969 | 5.00 | 77% |
M6 tap drill: 5.0 mm (0.1969 in / 5.00 mm), 77% thread% thread = 76.98 × (major − drill) ÷ pitch, the metric form of (major − drill) ÷ (1.299 × pitch) × 100. Standard drills are taken from published charts and checked against this formula on every build.