1. What is Tap Drill Size?

The tap drill size is the diameter of the hole that should be drilled before tapping threads. This calculator provides the size for approximately 75% thread engagement, which is standard for most applications.

2. How Does the Calculator Work?

The calculator uses the simple formula:

Where:

• Major Diameter — The largest diameter of the thread (mm)
• Pitch — The distance between thread crests (mm)

Explanation: This formula provides a tap drill size that will create about 75% thread engagement, which is the standard for most applications.

3. Importance of Correct Tap Drill Size

Details: Using the correct tap drill size is crucial for creating strong threads that won't strip easily while avoiding excessive torque requirements during tapping.

4. Using the Calculator

Tips: Enter the major diameter and pitch in millimeters. Both values must be positive numbers. The result is the recommended drill size for 75% thread engagement.

5. Frequently Asked Questions (FAQ)

Q1: Why 75% thread engagement?
A: 75% provides an optimal balance between thread strength and ease of tapping. Higher percentages increase strength but make tapping difficult.

Q2: What if I need different thread engagement?
A: For higher engagement, subtract less than the full pitch. For lower engagement, subtract more than the pitch.

Q3: Does this work for all thread types?
A: This works well for metric threads. For imperial threads, use the formula: Major Diameter - (1.0829 × Pitch).

Q4: How precise does the drill size need to be?
A: Within 0.05mm is generally acceptable for most applications.

Q5: What about thread depth?
A: The drill should be slightly deeper than the required thread depth to account for the cone at the drill point.