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Metric Threads: Overview and Usage

Close-up of a wrench and screwdriver on a metal surface, intended for metric threading tasks

What Are Metric Threads?

Metric threads are a standardised system of screw thread profiles used globally (primarily outside the U.S.) for fastening components. They are defined by ISO standards (e.g., ISO 68, ISO 261, ISO 965), with dimensions expressed in millimetres. A metric thread is typically noted as MxP, where M is the nominal diameter and P is the pitch (distance between threads).

Example:

M10 × 1.5 means a thread with a 10 mm major diameter and 1.5 mm pitch.

Thread Profile:

Thread angle: 60°
Thread form: triangular
Available in coarse, fine, and extra fine pitches

Where and How Metric Threads Are Used

1. Mechanical Fastening

Used in nuts, bolts, and screws to securely join machine parts.
Found in vehicles, manufacturing machinery, robotics, and appliances.

2. Precision Assembly

Fine pitch metric threads are preferred where tight tolerances or vibration resistance is important, such as in aerospace or electronics.

3. Construction and Structural Engineering

Coarse metric threads are used in building materials, supports, and infrastructure due to their robustness and ease of assembly.

4. Hydraulic and Pneumatic Systems

Metric threads help ensure sealed, high pressure connections in fluid and air systems (with special sealing techniques).

5. Global Standardisation

Since they are ISO standardised, metric threads are favoured in international production and engineering projects for compatibility and interoperability.

Close-up of a screw thread showcasing standardised profiles and intricate details of the threading design

Advantages

Global compatibility
Simplified sizing (all in metric units)
Standardised tolerances (e.g., 6H/6g fits)
Better vibration resistance in fine threads

Metric threads form the backbone of mechanical design and manufacturing worldwide, enabling consistent, strong, and reliable connections across industries.

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