Understanding the Metric Thread Angle

Metric threads are a widely used standard for threaded fasteners, like bolts and nuts. They are defined by the International Organization for Standardization (ISO) and are characterized by their pitch measured in millimeters and a specific thread form.

The Standard Metric Thread Profile

The standard metric screw thread, often referred to as the M profile, has a specific geometry designed for strength and interchangeability.

• Thread Form: It features a V-shaped thread form.
• Angle Measurement: The angle is typically measured between the external slope and the internal slope of the thread, when viewed in an axial section.
• Standard Angle: For the standard ISO metric screw thread, this angle is specified as 60°. This 60-degree angle is a fundamental characteristic of the metric thread system.

Why the 60° Angle?

The 60-degree thread angle provides a good balance between thread strength and ease of manufacturing. It allows for efficient power transmission and is widely adopted globally.

Analysis of Options

Let's look at why the other options are not the standard for metric threads:

• 90°: This angle is not standard for metric threads.
• 60°: This is the standard thread angle for metric threads.
• 30°: While some specific thread types might use variations, 30 degrees is not the standard angle for general metric threads.
• 120°: This angle is typically associated with Acme threads or other specialized thread forms, not standard metric threads.

Conclusion

The universally accepted thread angle for standard metric threads is 60°.