Thread Calculator: Pitch, Diameter and Tap Drill Size

Your details

Select the thread standard. Metric ISO uses millimetres; UNC and UNF use inches. Choose Custom to enter any nominal diameter and pitch directly.
Standard ISO metric coarse thread designation. The pitch is filled in automatically.
Most standard fasteners are single-start (1). Multi-start threads advance faster per revolution - lead = starts x pitch.
Choose the unit for all dimensional results. The underlying calculations always use millimetres internally.
Major diameter
10

Nominal outer diameter (crests of an external thread)

Pitch diameter9.0257
Minor diameter8.1597
Thread depth0.8119
Pitch1.5
Threads per inch (TPI)16.93
Lead1.5
Tap drill size8.5
Unitmm
Major diameter10
Pitch diameter9.0257
Minor diameter8.1597
Tap drill8.5

Metric ISO thread: major 10.0000 mm, pitch 1.5000 mm.

  • Major (nominal) diameter: 10.0000 mm. Minor diameter: 8.1597 mm.
  • Pitch is 1.5000 mm per thread, equivalent to 16.9 TPI.
  • Recommended tap drill diameter is 8.500 mm for approximately 75% thread engagement, which balances holding strength against tap breakage risk.

Next stepVerify tap drill size against a standard drill chart. For tapping blind holes, add extra depth (typically 1.5x thread diameter) to account for chip clearance.

 = Powered by OnlyCalculators