Metric Tap Drill Size Chart
Recommended Drill Sizes for Metric Threads
Selecting the correct tap drill size is an important step in producing accurate and reliable internal threads. The drill diameter directly affects thread engagement, tapping load, tool life, and the overall quality of the finished thread.
Metric threads are widely used in machining and manufacturing applications around the world. The reference chart below provides recommended drill sizes for common metric thread sizes and pitches, helping machinists quickly select an appropriate drill before tapping.
How to Read Metric Thread Sizes
A metric thread designation consists of the nominal thread diameter followed by the thread pitch.
For example:
M8 × 1.25
- M8 = Nominal thread diameter: 8 mm
- 1.25 = Thread pitch: 1.25 mm
- Recommended tap drill: 6.8 mm
Another example:
M10 × 1.5
- Nominal thread diameter: 10 mm
- Thread pitch: 1.5 mm
- Recommended tap drill: 8.5 mm
A simple reference formula commonly used for metric threads is:
Tap Drill Diameter ≈ Nominal Diameter − Thread Pitch
Example:
M10 × 1.5 → 10 − 1.5 = 8.5 mm
The actual drill size may vary depending on the workpiece material, required thread engagement, tap geometry, machining conditions, and applicable thread standard.
Metric Tap Drill Reference Chart
| Metric Thread | Recommended Drill |
|---|---|
| M2 × 0.4 | 1.60 mm |
| M2.5 × 0.45 | 2.10 mm |
| M3 × 0.5 | 2.50 mm |
| M3.5 × 0.6 | 2.90 mm |
| M4 × 0.7 | 3.30 mm |
| M5 × 0.8 | 4.20 mm |
| M6 × 1.0 | 5.00 mm |
| M7 × 1.0 | 6.00 mm |
| M8 × 1.25 | 6.80 mm |
| M9 × 1.25 | 7.80 mm |
| M10 × 1.5 | 8.50 mm |
| M11 × 1.5 | 9.50 mm |
| M12 × 1.75 | 10.30 mm |
| M14 × 2.0 | 12.00 mm |
| M16 × 2.0 | 14.00 mm |
| M18 × 2.5 | 15.50 mm |
| M20 × 2.5 | 17.50 mm |
| M22 × 2.5 | 19.50 mm |
| M24 × 3.0 | 21.00 mm |
| M27 × 3.0 | 24.00 mm |
| M30 × 3.5 | 26.50 mm |
| M33 × 3.5 | 29.50 mm |
| M36 × 4.0 | 32.00 mm |
| M39 × 4.0 | 35.00 mm |
| M42 × 4.5 | 37.50 mm |
| M45 × 4.5 | 40.50 mm |
| M48 × 5.0 | 43.00 mm |
The original PREX/CK TOOLS page also contains fine-pitch variants and maximum/minimum reference diameters for many of these sizes.
Important Considerations Before Tapping
The recommended drill diameter should be treated as a practical reference rather than a universal value for every application.
For best results, consider the workpiece material, tap type, thread tolerance, required thread engagement, machine rigidity, cutting conditions, and whether the operation uses a cutting tap or forming tap.
Forming taps require different pre-drilled hole diameters from conventional cutting taps. Always refer to the tap manufacturer's recommendations when available.
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Metric Tap Drill Size Chart | Drill Sizes for Metric Threads
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Metric tap drill size chart for common metric threads from M2 to M50. Find recommended drill diameters and practical information for accurate tapping operations.