Tap Hole Size Chart

Introduction

When drilling and tapping holes for screws, bolts, or fasteners, accuracy is essential to ensure proper threading and a secure fit. A tap hole size chart is a practical reference tap hole size chart that helps machinists, engineers, and DIY enthusiasts determine the correct drill size to use before tapping a thread. By following the chart, you can avoid issues such as stripped threads, weak connections, or oversized holes.

What is a Tap Hole Size Chart?

A tap hole size chart lists the recommended drill bit sizes for different screw thread sizes and types, such as metric or Unified Thread Standard (UTS). It provides a quick and reliable way to select the correct drill size based on the tap size you plan to use.

Importance of Using the Correct Tap Drill Size

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  Thread Strength: Ensures the right amount of material remains to create strong threads.

  
  


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  Accuracy: Prevents threading errors that can damage parts or tools.

  
  


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  Efficiency: Saves time and reduces material waste during machining.

  
  


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  Compatibility: Ensures screws and bolts fit securely without loosening.

  
  

Example Tap Hole Size Chart (Imperial and Metric)

Here’s a simplified reference for common thread sizes:

Imperial (UNC/UNF)

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  #4-40 → Drill Size #43 (0.0890")

  
  


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  #6-32 → Drill Size #36 (0.1065")

  
  


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  #8-32 → Drill Size #29 (0.1360")

  
  


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  1/4"-20 → Drill Size #7 (0.2010")

  
  


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  5/16"-18 → Drill Size F (0.2570")

  
  

Metric

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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 Tapping Holes

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  Always use cutting fluid to reduce friction and heat.

  
  


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  Drill at the recommended speed for the material type.

  
  


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  Back out the tap periodically to clear chips.

  
  


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  Use the correct tap type (taper, plug, or bottoming) for your application.

  
  

Conclusion

A tap hole size chart is a valuable tool that ensures precision, durability, and efficiency in threading operations. Whether you are working on metal, plastic, or wood, referencing the correct drill size before tapping prevents costly mistakes and guarantees a secure fit for fasteners.