Introduction

Tapping is the process of cutting threads into a drilled hole so that a screw or bolt can be fastened securely. Choosing the correct drill size is essential for producing strong, precise threads. A tap hole size chart acts as a quick guide, matching tap sizes with the right drill bit sizes to disadvantages of sand casting ensure reliable results.

Why the Right Tap Drill Size Matters

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  Prevents Stripped Threads: Too large a hole results in weak threads, while too small a hole can damage the tap.

  
  


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  Improves Fit: Ensures bolts and screws seat properly.

  
  


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  Saves Tools: Reduces the risk of breaking taps during threading.

  
  


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  Boosts Efficiency: Helps machinists and DIY users work faster without trial and error.

  
  

Common Imperial Tap Drill Sizes

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  #6-32 UNC → Drill Size #36 (0.1065")

  
  


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  #8-32 UNC → Drill Size #29 (0.1360")

  
  


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  1/4"-20 UNC → Drill Size #7 (0.2010")

  
  


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  5/16"-18 UNC → Drill Size F (0.2570")

  
  


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  3/8"-24 UNF → Drill Size Q (0.3320")

  
  

Common Metric Tap Drill Sizes

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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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  M10 x 1.5 → 8.5 mm drill

  
  

Best Practices for Drilling and Tapping

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  Always use a sharp drill bit for accurate holes.

  
  


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  Apply tapping oil or cutting fluid to reduce friction.

  
  


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  Keep the tap straight to avoid crooked threads.

  
  


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  Use the right tap (taper, plug, or bottoming) depending on hole depth.

  
  

Conclusion

A tap hole size chart is an indispensable reference that ensures proper thread cutting, strong fastening, and longer tool life. By using the correct drill bit for each tap size, you guarantee efficiency and precision in both industrial and DIY applications.