Introduction

In machining and metalworking, accurate threading begins with the right hole size. A tap hole size chart provides the recommended drill sizes for different taps, ensuring that threads are cut cleanly and securely. Without this guide, holes may be drilled too large or too small, leading bronce vs laton to weak or damaged threads.

Benefits of Using a Tap Hole Size Chart

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  Accuracy: Matches drill bits to tap sizes for precise threads.

  
  


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  Strength: Ensures the proper engagement of screws and bolts.

  
  


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  Efficiency: Saves time by removing guesswork during setup.

  
  


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  Versatility: Covers both metric and imperial thread standards.

  
  

Example Drill Sizes for Common Taps

Imperial (UNC/UNF)

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  #4-40 UNC → Drill Size #43 (0.089")

  
  


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  #10-32 UNF → Drill Size #21 (0.159")

  
  


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  1/4"-20 UNC → Drill Size #7 (0.201")

  
  


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  5/16"-18 UNC → Drill Size F (0.257")

  
  


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  1/2"-13 UNC → Drill Size 27/64" (0.4219")

  
  

Metric (Coarse)

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  M3 x 0.5 → 2.5 mm drill

  
  


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  M4 x 0.7 → 3.3 mm drill

  
  


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  M5 x 0.8 → 4.2 mm drill

  
  


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  M6 x 1.0 → 5.0 mm drill

  
  


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  M8 x 1.25 → 6.8 mm drill

  
  

Tips for Best Results

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  Always center-punch the hole location before drilling.

  
  


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  Use cutting oil to reduce friction and improve thread quality.

  
  


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  Clear chips regularly by reversing the tap during cutting.

  
  


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  Select the correct style of tap (taper, plug, or bottoming) depending on hole depth.

  
  

Conclusion

A tap hole size chart is a simple yet essential tool for machinists, engineers, and DIY users. It guarantees accuracy, durability, and consistency in threading operations, whether working with imperial or metric