Tap Drill Size

The Myth of 100% Threads

A common misconception is that threads should be cut to 100% engagement for maximum strength. In reality, testing shows that thread strength only increases marginally above 60% engagement, while the torque required to turn the tap increases exponentially.

Aiming for 100% threads usually results in broken taps, especially in tough materials like stainless steel or titanium, with almost no gain in fastener pull-out strength.

Form Taps vs. Cut Taps

This calculator is specifically for cutting taps (which remove material to form the thread). If you are using a form tap (roll tap), the physics change entirely. Form taps displace material rather than removing it, meaning they require a significantly larger starting hole.