For a standard 1/4-20 UNC tap, you should use a #7 drill bit, which is 0.201 inch in diameter.

Quick Scoop

  • Tap size: 1/4-20 UNC (¼ inch diameter, 20 threads per inch).
  • Recommended tap drill: #7 drill bit (0.201") for cutting taps in most metals.
  • Common substitute if you do not have numbered bits: 13/64" (0.2031") , acceptable for general-purpose work but with slightly less thread engagement.
  • For harder materials or critical, load‑bearing threads, stick with the #7 for better thread strength and lower risk of tap breakage.

Simple rule of thumb

For “what size drill bit for 1/4 20 tap,” the go‑to answer in charts and machining guides is: Use a #7 drill bit (0.201").

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Learn what size drill bit for 1/4 20 tap you need: the standard is a #7 drill bit (0.201"), with 13/64" as a common substitute, plus quick tips for stronger threads.

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