What Is The Metric Threads Of Fastener?

Metric threads on fasteners refer to the standardized thread design used globally for screws, bolts, nuts, and other types of fasteners that adhere to the metric system. This system of threads is defined by the International Organization for Standardization (ISO), with the most common standards being ISO 68-1, ISO 261, ISO 262, and ISO 965 for metric screw threads.

The key characteristics of metric threads include:

Diameter: This is the nominal diameter of the thread, typically expressed in millimeters (mm). For bolts and screws, it’s the outer diameter of the threads, while for nuts, it’s the inner diameter.

Pitch: This is the distance between adjacent threads, also measured in millimeters. In the metric system, the pitch can be coarse or fine. Coarse threads are more common and have a larger pitch, whereas fine threads have a smaller pitch, providing a higher degree of precision and strength.

Profile: The thread profile for metric threads is generally a symmetrical V-shape with a 60-degree angle. This standardized profile ensures compatibility and interchangeability between fasteners from different manufacturers.

Thread Tolerance: This specifies the permissible limits for the dimensions of threads, ensuring a proper fit between mating components. Tolerance classes for metric threads are defined by ISO standards, indicating the level of precision of the thread.

Designation: Metric thread sizes are designated by an “M” followed by the nominal diameter and the pitch, separated by an “x”. For example, M8x1.25 represents a metric thread with an 8mm nominal diameter and a 1.25mm pitch. If the pitch is not specified, it indicates a coarse thread.

Metric threads are widely used because they offer a standardized, precise, and easy-to-use system for fastening components in mechanical and engineering applications worldwide. The use of metric threads facilitates international trade and manufacturing, as the standardized dimensions allow for compatibility across components made in different countries.

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