Differences and Requirements of Three Major Screw Threads of Fasteners

The fastener provided by QISHINE is important components in many mechanical and structural applications. They are used to join two or more objects together and are available in various types and sizes. Three of the most commonly used screw threads for fasteners are Metric, American, and British. Each type of screw thread has its own unique characteristics, differences, and requirements.

Metric Screw Threads
Metric screw threads are based on the International System of Units (SI) and are commonly used in Europe and Asia. They are designated by the thread pitch, which is the distance between each thread crest measured along the axis of the screw. The thread angle is 60 degrees, and the thread form is a symmetrical V-shape.

The major difference between Metric screw threads and American or British screw threads is the measurement system used. Metric screw threads are measured in millimeters, while American and British screw threads are measured in inches.

American Screw Threads
American screw threads are commonly used in the United States, Canada, and other countries that follow the Unified Thread Standard (UTS). There are two types of UTS screw threads: coarse and fine. Coarse threads have fewer threads per inch and are used for quick assembly, while fine threads have more threads per inch and are used for greater precision and strength.

The thread angle for American screw threads is 60 degrees, and the thread form is a flattened V-shape. The thread pitch is measured in threads per inch (TPI), and the diameter is measured in inches. American screw threads are also differentiated by their thread series, which refers to the diameter and pitch combination. Common thread series include UNC (Unified Coarse), UNF (Unified Fine), and UNEF (Unified Extra Fine).

British Screw Threads
British screw threads are commonly used in the United Kingdom, Australia, and New Zealand. There are two main types of British screw threads: Whitworth and British Standard Whitworth (BSW). The thread angle for Whitworth threads is 55 degrees, while the thread angle for BSW threads is 60 degrees. The thread form for both types of threads is a rounded V-shape.

Like American screw threads, British screw threads are also measured in inches. The thread pitch is measured in TPI, and the diameter is measured in fractions of an inch. Common thread types include BSW (British Standard Whitworth), BSF (British Standard Fine), and BA (British Association).

Requirements of Screw Threads

The requirements for screw threads vary depending on the application and the type of screw thread used. Some of the common requirements include:

Thread Pitch: The thread pitch should be specified accurately to ensure proper mating of the threads.

Thread Angle: The thread angle should be uniform to ensure proper torque transmission and prevent stripping of the threads.

Thread Form: The thread form should be specified accurately to ensure proper fit and engagement of the threads.

Tolerance: The tolerance for the screw threads should be specified accurately to ensure proper mating of the threads and prevent thread damage.

Surface Finish: The surface finish of the screw threads should be specified accurately to ensure proper sealing and prevent leakage.

In conclusion, the differences and requirements of Metric, American, and British screw threads for fasteners are significant. The measurement system used, the thread angle, and the thread form are the primary differences between the three types of screw threads. It is essential to select the appropriate screw thread based on the application and the requirements of the fastener to ensure proper fit, engagement, and torque transmission.

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