Metric Thread Pitch Chart
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- **Title:** Metric Thread Pitch Chart | M1.6 to M64 | Coarse & Fine Pitch | Tap Drill Sizes- Meta Description: Complete metric thread pitch chart for ISO standard threads M1.6 through M64. Includes coarse and fine pitch, major diameter, tap drill sizes, and clearance hole specifications.
- Keywords: metric thread pitch chart, ISO metric threads, metric tap drill chart, metric clearance holes, coarse pitch, fine pitch, M6 thread pitch, M8 thread pitch, metric bolt sizes
Introduction
Metric threads follow the ISO 68-1 standard and are used worldwide as the primary thread system outside of North America. This comprehensive chart covers both coarse pitch (standard) and fine pitch variants from M1.6 through M64.
Metric thread designations follow the format M[diameter]×[pitch]. For example, M8×1.25 indicates an 8mm major diameter with 1.25mm pitch. When pitch is omitted (e.g., "M8"), the coarse pitch is assumed.
Metric Coarse Pitch Thread Chart
Coarse pitch threads are the default metric thread series. They're used for general-purpose fastening and are assumed when no pitch is specified.
Small Sizes (M1.6 - M6)
| Size | Major Dia (mm) | Pitch (mm) | Tap Drill (mm) | Close Fit Clearance | Free Fit Clearance |
|---|---|---|---|---|---|
| M1.6 | 1.60 | 0.35 | 1.25 | 1.7 | 1.8 |
| M2 | 2.00 | 0.40 | 1.60 | 2.2 | 2.4 |
| M2.5 | 2.50 | 0.45 | 2.05 | 2.7 | 2.9 |
| M3 | 3.00 | 0.50 | 2.50 | 3.2 | 3.4 |
| M3.5 | 3.50 | 0.60 | 2.90 | 3.7 | 3.9 |
| M4 | 4.00 | 0.70 | 3.30 | 4.3 | 4.5 |
| M5 | 5.00 | 0.80 | 4.20 | 5.3 | 5.5 |
| M6 | 6.00 | 1.00 | 5.00 | 6.4 | 6.6 |
Medium Sizes (M7 - M16)
| Size | Major Dia (mm) | Pitch (mm) | Tap Drill (mm) | Close Fit Clearance | Free Fit Clearance |
|---|---|---|---|---|---|
| M7 | 7.00 | 1.00 | 6.00 | 7.4 | 7.6 |
| M8 | 8.00 | 1.25 | 6.80 | 8.4 | 9.0 |
| M10 | 10.00 | 1.50 | 8.50 | 10.5 | 11.0 |
| M12 | 12.00 | 1.75 | 10.20 | 13.0 | 14.0 |
| M14 | 14.00 | 2.00 | 12.00 | 15.0 | 16.0 |
| M16 | 16.00 | 2.00 | 14.00 | 17.0 | 18.0 |
Large Sizes (M18 - M36)
| Size | Major Dia (mm) | Pitch (mm) | Tap Drill (mm) | Close Fit Clearance | Free Fit Clearance |
|---|---|---|---|---|---|
| M18 | 18.00 | 2.50 | 15.50 | 19.0 | 20.0 |
| M20 | 20.00 | 2.50 | 17.50 | 21.0 | 22.0 |
| M22 | 22.00 | 2.50 | 19.50 | 23.0 | 24.0 |
| M24 | 24.00 | 3.00 | 21.00 | 25.0 | 26.0 |
| M27 | 27.00 | 3.00 | 24.00 | 28.0 | 30.0 |
| M30 | 30.00 | 3.50 | 26.50 | 31.0 | 33.0 |
| M33 | 33.00 | 3.50 | 29.50 | 34.0 | 36.0 |
| M36 | 36.00 | 4.00 | 32.00 | 37.0 | 39.0 |
Extra Large Sizes (M39 - M64)
| Size | Major Dia (mm) | Pitch (mm) | Tap Drill (mm) | Close Fit Clearance | Free Fit Clearance |
|---|---|---|---|---|---|
| M39 | 39.00 | 4.00 | 35.00 | 40.0 | 42.0 |
| M42 | 42.00 | 4.50 | 37.50 | 43.0 | 45.0 |
| M45 | 45.00 | 4.50 | 40.50 | 46.0 | 48.0 |
| M48 | 48.00 | 5.00 | 43.00 | 50.0 | 52.0 |
| M52 | 52.00 | 5.00 | 47.00 | 54.0 | 56.0 |
| M56 | 56.00 | 5.50 | 50.50 | 58.0 | 62.0 |
| M60 | 60.00 | 5.50 | 54.50 | 62.0 | 66.0 |
| M64 | 64.00 | 6.00 | 58.00 | 66.0 | 70.0 |
Metric Fine Pitch Thread Chart
Fine pitch threads have a smaller pitch than the coarse series for the same diameter. They're specified when vibration resistance, fine adjustment, or higher strength in thin-walled materials is needed.
Small Sizes (M3 - M8)
| Size | Major Dia (mm) | Fine Pitch Options | Primary Tap Drill | Secondary Tap Drill |
|---|---|---|---|---|
| M3×0.35 | 3.00 | 0.35 | 2.65 | — |
| M4×0.5 | 4.00 | 0.5 | 3.50 | — |
| M5×0.5 | 5.00 | 0.5 | 4.50 | — |
| M6×0.5 | 6.00 | 0.5 | 5.50 | — |
| M6×0.75 | 6.00 | 0.75 | 5.25 | — |
| M7×0.75 | 7.00 | 0.75 | 6.25 | — |
| M8×0.5 | 8.00 | 0.5 | 7.50 | — |
| M8×0.75 | 8.00 | 0.75 | 7.25 | — |
| M8×1.0 | 8.00 | 1.0 | 7.00 | — |
Medium Sizes (M10 - M20)
| Size | Major Dia (mm) | Fine Pitch Options | Primary Tap Drill | Secondary Tap Drill |
|---|---|---|---|---|
| M10×0.75 | 10.00 | 0.75 | 9.25 | — |
| M10×1.0 | 10.00 | 1.0 | 9.00 | — |
| M10×1.25 | 10.00 | 1.25 | 8.80 | — |
| M12×1.0 | 12.00 | 1.0 | 11.00 | — |
| M12×1.25 | 12.00 | 1.25 | 10.80 | — |
| M12×1.5 | 12.00 | 1.5 | 10.50 | — |
| M14×1.0 | 14.00 | 1.0 | 13.00 | — |
| M14×1.25 | 14.00 | 1.25 | 12.80 | — |
| M14×1.5 | 14.00 | 1.5 | 12.50 | — |
| M16×1.0 | 16.00 | 1.0 | 15.00 | — |
| M16×1.5 | 16.00 | 1.5 | 14.50 | — |
| M18×1.0 | 18.00 | 1.0 | 17.00 | — |
| M18×1.5 | 18.00 | 1.5 | 16.50 | — |
| M18×2.0 | 18.00 | 2.0 | 16.00 | — |
| M20×1.0 | 20.00 | 1.0 | 19.00 | — |
| M20×1.5 | 20.00 | 1.5 | 18.50 | — |
| M20×2.0 | 20.00 | 2.0 | 18.00 | — |
Large Sizes (M22 - M64)
| Size | Major Dia (mm) | Fine Pitch Options | Primary Tap Drill | Notes |
|---|---|---|---|---|
| M22×1.5 | 22.00 | 1.5 | 20.50 | Common automotive |
| M22×2.0 | 22.00 | 2.0 | 20.00 | — |
| M24×1.5 | 24.00 | 1.5 | 22.50 | — |
| M24×2.0 | 24.00 | 2.0 | 22.00 | Common machinery |
| M27×1.5 | 27.00 | 1.5 | 25.50 | — |
| M27×2.0 | 27.00 | 2.0 | 25.00 | — |
| M30×1.5 | 30.00 | 1.5 | 28.50 | — |
| M30×2.0 | 30.00 | 2.0 | 28.00 | — |
| M30×3.0 | 30.00 | 3.0 | 27.00 | — |
| M33×2.0 | 33.00 | 2.0 | 31.00 | — |
| M33×3.0 | 33.00 | 3.0 | 30.00 | — |
| M36×1.5 | 36.00 | 1.5 | 34.50 | — |
| M36×2.0 | 36.00 | 2.0 | 34.00 | — |
| M36×3.0 | 36.00 | 3.0 | 33.00 | — |
| M39×2.0 | 39.00 | 2.0 | 37.00 | — |
| M39×3.0 | 39.00 | 3.0 | 36.00 | — |
| M42×2.0 | 42.00 | 2.0 | 40.00 | — |
| M42×3.0 | 42.00 | 3.0 | 39.00 | — |
| M45×2.0 | 45.00 | 2.0 | 43.00 | — |
| M45×3.0 | 45.00 | 3.0 | 42.00 | — |
| M48×2.0 | 48.00 | 2.0 | 46.00 | — |
| M48×3.0 | 48.00 | 3.0 | 45.00 | — |
| M52×2.0 | 52.00 | 2.0 | 50.00 | — |
| M52×3.0 | 52.00 | 3.0 | 49.00 | — |
| M56×2.0 | 56.00 | 2.0 | 54.00 | — |
| M56×4.0 | 56.00 | 4.0 | 52.00 | — |
| M60×2.0 | 60.00 | 2.0 | 58.00 | — |
| M60×4.0 | 60.00 | 4.0 | 56.00 | — |
| M64×2.0 | 64.00 | 2.0 | 62.00 | — |
| M64×4.0 | 64.00 | 4.0 | 60.00 | — |
Tap Drill Calculation Formula
For metric threads, the tap drill size can be calculated:
Tap Drill = Major Diameter − Pitch
This formula produces approximately 75% thread engagement, which is the standard for most applications.
Examples:
- M8×1.25: Tap drill = 8.0 − 1.25 = 6.75mm (use 6.8mm)
- M10×1.5: Tap drill = 10.0 − 1.5 = 8.5mm
- M12×1.75: Tap drill = 12.0 − 1.75 = 10.25mm (use 10.2mm)
Thread Engagement Percentages
| Thread % | Tap Drill Formula | Use Case |
|---|---|---|
| 60% | Dia − (0.8 × Pitch) | Easy tapping, soft materials |
| 75% | Dia − Pitch | Standard (recommended) |
| 85% | Dia − (1.1 × Pitch) | Maximum strength |
Clearance Hole Standards (ISO 273)
ISO 273 defines three categories of clearance holes for metric fasteners:
Clearance Hole Categories
| Fit Type | Description | Use Case |
|---|---|---|
| Fine (H12) | Close clearance | Precision alignment |
| Medium (H13) | Standard clearance | General assembly |
| Coarse (H14) | Generous clearance | Easy assembly, misalignment |
Complete Clearance Hole Table
| Bolt Size | Fine Fit (H12) | Medium Fit (H13) | Coarse Fit (H14) |
|---|---|---|---|
| M1.6 | 1.7 | 1.8 | 2.0 |
| M2 | 2.2 | 2.4 | 2.6 |
| M2.5 | 2.7 | 2.9 | 3.1 |
| M3 | 3.2 | 3.4 | 3.6 |
| M4 | 4.3 | 4.5 | 4.8 |
| M5 | 5.3 | 5.5 | 5.8 |
| M6 | 6.4 | 6.6 | 7.0 |
| M8 | 8.4 | 9.0 | 10.0 |
| M10 | 10.5 | 11.0 | 12.0 |
| M12 | 13.0 | 14.0 | 15.0 |
| M14 | 15.0 | 16.0 | 17.0 |
| M16 | 17.0 | 18.0 | 19.0 |
| M18 | 19.0 | 20.0 | 21.0 |
| M20 | 21.0 | 22.0 | 24.0 |
| M22 | 23.0 | 24.0 | 26.0 |
| M24 | 25.0 | 26.0 | 28.0 |
| M27 | 28.0 | 30.0 | 32.0 |
| M30 | 31.0 | 33.0 | 35.0 |
| M33 | 34.0 | 36.0 | 38.0 |
| M36 | 37.0 | 39.0 | 42.0 |
| M42 | 43.0 | 45.0 | 48.0 |
| M48 | 50.0 | 52.0 | 56.0 |
| M56 | 58.0 | 62.0 | 66.0 |
| M64 | 66.0 | 70.0 | 74.0 |
Metric Thread Tolerance Classes
External Threads (Bolts/Screws)
| Class | Tolerance | Application |
|---|---|---|
| 4g | Tight | Interference fit after plating |
| 6g | Standard | General purpose (most common) |
| 8g | Loose | Hot-dip galvanized, dirty environments |
Internal Threads (Nuts/Tapped Holes)
| Class | Tolerance | Application |
|---|---|---|
| 5H | Tight | Precision fits |
| 6H | Standard | General purpose (most common) |
| 7H | Loose | Allowance for coatings |
Standard Fit Combinations
| Application | External | Internal | Notes |
|---|---|---|---|
| General use | 6g | 6H | Most common combination |
| Precision | 4g | 5H | Close tolerance |
| Plated | 6g | 6H | Class before plating |
| Galvanized | 8g | 7H | Accommodates thick coating |
Practical Tips
Identifying Metric Thread Size
1. Measure major diameter with calipers (outer thread diameter)
2. Measure pitch with thread gauge or by counting threads over 10mm
3. Match to chart − M-diameter × pitch
Common Metric to Imperial Near-Equivalents
| Metric | Major Dia | Near Imperial | Major Dia |
|---|---|---|---|
| M3 | 3.0mm | #4-40 | 2.8mm |
| M4 | 4.0mm | #8-32 | 4.2mm |
| M5 | 5.0mm | #10-24 | 4.8mm |
| M6 | 6.0mm | 1/4"-20 | 6.4mm |
| M8 | 8.0mm | 5/16"-18 | 7.9mm |
| M10 | 10.0mm | 3/8"-16 | 9.5mm |
| M12 | 12.0mm | 1/2"-13 | 12.7mm |
Warning: These are NOT interchangeable. The threads are different and will not mate properly.
When to Use Fine vs Coarse Pitch
- Coarse (default): General assembly, softer materials, dirty environments
- Fine: Vibration resistance, fine adjustment, thin-wall tapping, higher strength
Frequently Asked Questions
What does "M8×1.25" mean?
M8×1.25 indicates a metric thread with 8mm major diameter and 1.25mm pitch. The "M" stands for metric. If just "M8" is written without pitch, coarse pitch (1.25mm) is assumed.
How do I calculate the tap drill size for a metric thread?
Subtract the pitch from the major diameter. For M10×1.5: 10 − 1.5 = 8.5mm tap drill. This gives approximately 75% thread engagement, which is the industry standard.
What's the difference between coarse and fine pitch?
Coarse pitch has larger thread spacing and is the default. Fine pitch has smaller spacing, providing more threads per unit length. Fine pitch offers better vibration resistance and finer adjustment but is more prone to cross-threading and stripping.
Can I use an M6 bolt in a 1/4" hole?
No. While M6 (6.0mm) and 1/4" (6.35mm) are close in diameter, the thread pitches are completely different. M6×1.0 is not compatible with 1/4"-20 UNC. Never mix metric and imperial threads.
What clearance hole should I drill for an M8 bolt?
For standard assembly, use 9.0mm (medium fit). For precise alignment, use 8.4mm (fine fit). For easy assembly with possible misalignment, use 10.0mm (coarse fit).
How do I identify an unknown metric thread?
Measure the major diameter with calipers (e.g., 8.0mm). Then use a thread pitch gauge to measure the pitch (e.g., 1.25mm). The thread is M8×1.25, or simply M8 if it's the coarse pitch.
Related Resources
- [Imperial Thread Pitch Chart](/reference/thread-pitch-chart-imperial)
- [UNC vs UNF Selection Guide](/reference/unc-vs-unf-guide)
- [Thread Engagement Calculator](/reference/thread-engagement-chart)
- [Thread Identification Guide](/reference/thread-identification-guide)
Last Updated: January 2025
Technical data based on ISO 68-1 and ISO 261 metric thread standards.