About TapDrill

TapDrill is a free workshop reference for machinists, makers and DIYers. Every number is calculated from published standards rather than copied from other charts. Inch threads use ASME B1.1, metric threads ISO 261/724, drill sizes ASME B94.11M, and clearance holes ISO 273. That way every page shows the same values and can be checked.

The site is built and maintained with the help of automated tools and is reviewed by its owner. Recommended inch tap drills are the standard drill closest to 75% thread. We cross-checked them against common published tap drill charts.

Corrections

Found a mistake? A contact address will be published here when the site moves to its own domain.

Disclaimer

For general shop use. For aerospace, pressure, lifting or other safety-critical work, follow your engineering standard and the tool maker's data.