ISO 68-1 is the international standard that defines the fundamental profile and geometry of metric screw threads. Metric threads are widely used in mechanical and industrial applications due to their standardization and compatibility across industries.
This standard establishes the triangular thread form with a 60° thread angle, specifying crest and root rounding for optimal performance. It serves as the basis for other metric thread standards, such as ISO 261, ISO 724, and ISO 965.
Technical Specifications
ISO 68-1 specifies the basic profile of metric threads, ensuring compatibility and standardization across different applications.
Key Thread Profile Parameters:
- Thread Angle (α): 60°
- Crest Rounding (r₁): 0.125 × P (Pitch)
- Root Rounding (r₂): 0.144 × P (Pitch)
- Major Diameter (d): The largest diameter of the external thread
- Minor Diameter (d₁): The smallest diameter of the internal thread
These parameters ensure a strong and reliable connection in threaded components.
ISO 68-1 Thread Dimension Table
The table below provides nominal diameters, pitch values, major and minor diameters, and recommended drill sizes for internal threads.
Standard Metric Thread Dimensions (ISO 68-1)
| Nominal Diameter (M) | Pitch (P) (mm) | Major Diameter (d) (mm) | Minor Diameter (d₁) (mm) | Recommended Drill Size (mm) |
|---|---|---|---|---|
| M1 | 0.25 | 1.00 | 0.75 | 0.8 |
| M2 | 0.40 | 2.00 | 1.60 | 1.7 |
| M3 | 0.50 | 3.00 | 2.40 | 2.5 |
| M4 | 0.70 | 4.00 | 3.30 | 3.4 |
| M5 | 0.80 | 5.00 | 4.20 | 4.3 |
| M6 | 1.00 | 6.00 | 5.00 | 5.2 |
| M8 | 1.25 | 8.00 | 6.75 | 6.8 |
| M10 | 1.50 | 10.00 | 8.50 | 8.8 |
| M12 | 1.75 | 12.00 | 10.20 | 10.5 |
| M16 | 2.00 | 16.00 | 13.90 | 14.0 |
| M20 | 2.50 | 20.00 | 17.30 | 17.5 |
| M24 | 3.00 | 24.00 | 20.90 | 21.0 |
🔹 Note: The drill size is recommended for internal thread cutting.
Applications
Metric threads standardized by ISO 68-1 are used in mechanical engineering, automotive industries, construction, aerospace, and general manufacturing. Their main advantage is global compatibility, making them a preferred choice worldwide.
Related Metric Thread Standards
After reviewing ISO 68-1, you may also find these related metric thread standards useful:
- ISO 261 – Standard Metric Thread Sizes (Defines the standard metric thread diameters and pitches)
- ISO 262 – Preferred Metric Thread Sizes (Specifies the most commonly used metric thread sizes)
- ISO 724 – Basic Dimensions of Metric Threads (Defines the fundamental dimensions of metric threads)
- ISO 965 – Metric Thread Tolerances (Specifies tolerances for external and internal metric threads)
- ISO 1502 – Thread Gauges for Metric Threads (Describes the use of gauges for thread inspection)
These links allow users to navigate easily between related standards.
Important Notice on Standards Validity
This information is for reference purposes only. Users should consult official sources and updated standards to ensure compliance with current regulations. The validity of standards may change over time, so it is recommended to verify them through recognized engineering and standardization organizations (ISO, DIN, ANSI, ASME, etc.).
Check with relevant standardization bodies in your region to confirm whether a specific standard is still valid and applicable. Regulations and industry requirements may vary based on region and application.