Calculate approximate internal thread percentage from major diameter, pitch and tap drill diameter for metric and inch threads.
Enter the thread dimensions and tap drill size to calculate.
What does thread percentage mean? It is an approximate measure of how much of the theoretical basic thread depth is represented by the internal thread.
How does tap-drill size affect thread percentage? A smaller tap drill produces a deeper internal thread and a higher theoretical thread percentage. A larger drill produces a shallower thread.
Does thread percentage equal thread strength? No. Thread strength also depends on engagement length, materials, diameter, pitch, thread quality and the type of loading.
Why is 100% thread not always desirable? Increasing thread percentage can substantially increase tapping torque while providing diminishing practical increases in thread shear strength.
Can this calculate metric threads? Yes. Enter major diameter, pitch and tap-drill diameter.
Can this calculate inch threads? Yes. Enter major diameter and TPI. The calculator converts TPI to pitch.
Does the calculator account for thread tolerance? No. It is a geometric approximation. Thread class, tolerance and tap geometry must be considered separately.
Can I use this to select a production tap drill? Use the result as a reference calculation. For production machining, verify the drill size against the applicable thread standard and tap manufacturer's recommendation.