To tap an M20 thread (pitch 2.5 mm), drill a 17.5 mm hole for standard 6H tolerance. Use 17.9 mm for a looser 7H fit. M20 taps are common in large anchor bolts and heavy machinery foundations.
| Tolerance class | Drill diameter | Pitch | Thread depth |
|---|---|---|---|
| 6H (standard) | 17.5 mm | 2.5 mm | 25–32 mm |
| 7H (loose) | 17.9 mm | 2.5 mm | 25–32 mm |
| 4H (tight) | 17.2 mm | 2.5 mm | 25–32 mm |
Fine pitch M20×1.5 variant available in Handbook Locksmith app.
FAQ
17.5 mm drill for standard M20 thread (6H tolerance, pitch 2.5 mm).
Full M20 thread data in the app
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