Tap Drill Size Calculator

For Kennametal Holemaking Application


! These calculations are based upon theoretical values and are only intended for planning purposes. Actual results will vary. No responsibility from Kennametal is assumed.

For Cutting Taps

Cutting Tap Parameters         

    Major diameter:     in       Calculate this below
    Threads per inch:      
    Thread height:     %    

    

Resulting hole size

Inch:     in.       Metric:     mm     


For Forming Taps

Forming Tap Parameters         

    Major diameter:     in       Calculate this below
    Threads per inch:  
    Thread height:     %    

    

Resulting hole size

Inch:     in.       Metric:     mm     


Calculate major diameter for Tap Drill Size

    Machine screw #:             
    Major diameter:     inch       mm


Suggested Percentages of Full Thread in Tapped Holes

A common internal thread, drilled so that it results in 50% of full thread will break the external thread, before the internal thread will strip.  A common internal thread drilled out so that it contains 100% of full thread is only 5% stronger than a 75% height of thread, yet it requires 3 times the power to tap.
  Deep Hole Tapping Average Commercial Work Thin cross sections
Hard or Tough Materials 55% - 65% 60% - 70%  
Cast Steel Forgings
High Temperature Alloys
Alloy Steels
Stainless Steels		  
Free Cutting Materials 60% - 70% 65% - 75% 75% - 85%
Aluminum
Brass
Bronze
Gray Cast Iron
Copper
Low Carbon and Free
Machining Steels