Metric Thread Drilling Calculator

Select the metric thread size to calculate the required drilling diameter:
Recommended Drill Bit Size:

Thread Size Pitch (mm) Major Diameter (mm) Minor Diameter (mm)
Metric Thread Drilling Guide

Metric Thread Drilling Guide

Your go-to chart for finding the right drill diameter for threading

Introduction

For metalworkers, selecting the correct drill bit diameter is essential when preparing to cut metric threads. Drilling the right-sized hole ensures a proper fit for the threaded insert, avoiding thread damage and ensuring the strength and stability of the finished piece. This helpful guide offers an easy-to-use metric thread chart, highlighting the key major and minor diameters for common metric threads.

Why Accurate Hole Sizes Matter

When you’re cutting threads, the diameter of the drilled hole must align with the thread’s specifications. An incorrect hole size can cause threads to be too loose or too tight, leading to poor engagement, thread damage, or weakened joints. Whether you’re working with bolts, nuts, or threaded inserts, understanding and applying the right drill size is a must for precision.

Metric Thread Drilling Chart: Major and Minor Diameters

The chart below outlines the necessary drill bit sizes for various metric threads. The chart includes both the major diameter (the outside diameter of the thread) and the minor diameter (the inner diameter of the thread), which are crucial for determining the correct drill bit for tapping or cutting threads into materials.

Thread Size (M) Thread Designation Pitch (mm) Drill Diameter (mm) Major Diameter (mm) Minor Diameter (mm)
M1 M1x0.25 0.25 0.982 0.982 0.729
M2 M2x0.4 0.4 1.981 1.981 1.567
M3 M3x0.5 0.5 2.980 2.980 2.459
M4 M4x0.7 0.7 3.978 3.978 3.242
M5 M5x0.8 0.8 4.976 4.976 4.134
M6 M6x1 1 5.974 5.974 4.917
M7 M7x1 1 6.974 6.974 5.917
M8 M8x1.25 1.25 7.972 7.972 6.647
M9 M9x1.25 1.25 8.972 8.972 7.647
M10 M10x1.5 1.5 9.968 9.968 8.376
M12 M12x1.75 1.75 11.970 11.970 10.106
M14 M14x2 2 13.960 13.960 11.835
M16 M16x2 2 15.960 15.960 13.835
M18 M18x2.5 2.5 17.960 17.960 15.294
M20 M20x2.5 2.5 19.960 19.960 17.294
M22 M22x2.5 2.5 21.960 21.960 19.294
M24 M24x3 3 23.950 23.950 20.752
M27 M27x3 3 26.950 26.950 23.752
M30 M30x3.5 3.5 29.950 29.950 26.211
M33 M33x3.5 3.5 32.970 32.970 29.211
M36 M36x4 4 35.940 35.940 31.670
M39 M39x4 4 38.940 38.940 34.670
M42 M42x4.5 4.5 41.940 41.940 37.129
M45 M45x4.5 4.5 44.940 44.940 40.129
M48 M48x5 5 47.930 47.930 42.587
M52 M52x5 5 51.930 51.930 46.587
M56 M56x5.5 5.5 55.930 55.930 50.046

How to Use the Chart

1. Select Thread Size: Find the metric thread size you plan to use (e.g., M6, M8, M10, etc.).

2. Check the Pitch: Determine the pitch, or the distance between threads, which can be found in your specifications.

3. Choose the Correct Drill Bit: Match the thread size and pitch to the chart’s recommended drill bit diameter.

Common Drill Size Mistakes to Avoid

Drilling too large a hole: Drilling a hole that is too large can cause the threads to be weak, making the fastening prone to failure.

Drilling too small a hole: A hole that is too small for the specified diameter will result in poorly formed threads or cause unnecessary stress on your tools.

Additional Threading Tips for Metalworkers

  • Use the Right Drill Bit: A standard twist drill bit works well for most applications, but for precise threading, you may also want to use a drill bit designed for tapping.
  • Consider Material Type: Harder materials (like steel) may require different drill sizes, as they resist cutting and threading more than softer materials.
  • Tapping Drills vs. Through-Hole Drills: If you are tapping a hole, always follow the drill sizes that correspond to the required tapping drill bit. For through-holes, the chart above should suffice.

Conclusion

For successful threading and metalworking projects, knowing the correct drill bit size is crucial. This metric thread drilling guide provides metalworkers with the exact drill diameters needed for various thread sizes, ensuring precise and secure thread cutting every time. Whether you are working on bolts, fasteners, or other metal components, this chart will make your project smoother and more accurate.

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