Calculate a basic metric tap drill size from nominal diameter and pitch.
Using the calculator
Enter values that match the tool, material and operation. Check the unit beside each field before calculating.
Calculation
Basic metric tap drill size = major diameter − pitch. Check the tap maker’s chart for production work.
Reading the result
The result follows the relationship shown on this page. Final shop settings also depend on material, tool geometry, workholding, machine capability, coolant and the actual cut.
Worked example
For example, an M10 × 1.5 basic metric relationship gives 8.5 mm tap drill size.