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Tap Drill Chart
I got sick of online tap drill charts giving you weird numbers for stuff - you know, you need a M3.5 hole, so just grab your 2.9mm drill! I don't happen to have one of those laying around - so I made my own!
The 100% - 50% columns correspond to thread engagement - how much of the thread is in contact with the material.
- For most purposes, use 75%.
- In plastic (and other soft materials), 100% can provide great strength.
- 50% will be easier to tap, and is what you should use in tougher materials (eg steel).
If it's a hole with depth at least 2 x diameter, you can use this to make it easier to tap, without giving up most of the strength.
TapDrillMath.ods
Metric Coarse Tap Drill Size
(Rounded to nearest 0.5mm)
| Size |
Pitch |
Inner Diameter |
100% |
75% |
50% |
Metric Fine Tap Drill Size
(Rounded to nearest 0.5mm)
| Size |
Pitch |
Inner Diameter |
100% |
75% |
50% |
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