Engineering Tools

Introduction:

Welcome to the Tap Drill Size Calculator. This calculator is primarily for machinist and fabricators who need to tap a hole for threads. You can select from the majority of standard sized bolts, both in imperial and metric measurements. If you have a custom project, there is a custom field to fill in major diameter and pitch for your thread.

How To Use:

Select which method you want to use with the radio buttons. Standard allows you to select from a variety of standard bolts. Custom allows you to input your own pitch and dimensions.

Thread engagement percentage is set to 75%, but should be adjusted down if tapping hard metals (ie. stainless, titanium). Higher engagement percentage means more of the threads are in contact. However, a higher thread engagement also means higher tapping torque needed. Higher torques can result in broken taps.

The results will show the perfect diameter to meet your selected thread engagement, and then followed by all the drill bits that are close to that. Results highlighted in green are within 2 percentage points of your selected thread engagement. Results highlighted in yellow are between 2-5 percentage points, and results highlighted in red are over 5 percentage points from your selected value.

You may not have the selected drill bit in your tool box. At the bottom, you can select a drill bit that you do have and solve to find your engagement percentage. These will also highlight in green, yellow, or red.

**Note: Values have been acquired from various sources. We cannot guarantee that all values are 100% correct.

Thank You

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