Tap Drill Size Calculator

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This tap drill size calculator helps determine the correct drill size before tapping threads.

It uses the tap size and threads per inch (TPI) to estimate the proper hole diameter.

Formula:

Drill Size = Tap Size − (1 / TPI)

Choosing the correct drill size ensures proper thread engagement and reduces the risk of tap breakage.

Example:

For a 1/4"-20 thread:

Drill Size ≈ 0.25 − (1 / 20) = 0.25 − 0.05 = 0.20 inches.

When to use this calculator:

Use this calculator to determine the correct drill size before tapping threads.

Machining tip:

Using the correct drill size prevents tap breakage and ensures proper thread engagement.

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• Material Weight Calculator

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