Classification of Screw Threads and How to Inspect Them.


The screw thread is crucial to the performance and lifespan of mechanical components. In the mechanical parts inspection, we should be familiar with the uses of various screw threads and how to properly inspect them to ensure that every detail of the product meets the drawings requirements.
Threads can be divided into several categories, including:
1. Coarse threads and fine threads: Coarse threads have larger pitch and fewer threads per inch, while fine threads have smaller pitch and more threads per inch.
2. Metric threads: These are standard threads used in most countries outside of the United States. They are defined by the International Organization for Standardization (ISO).
3. Imperial threads: These are standard threads used in the United States and the United Kingdom. They are defined by the British Standard Whitworth (BSW) and Unified Thread Standard (UTS).
4. Left-handed threads: These are threads that are threaded in the opposite direction of right-handed threads.
5. Square threads: These are four-sided threads used in applications that require high levels of precision and accuracy.
6. Acme threads: These are trapezoidal-shaped threads used in applications where high loads and low friction are required.
7. Buttress threads: These are threads with a flat top and a sloping bottom that are used in applications that require a high degree of resistance to side forces.
how to inspect the threads?
Thread inspection is the process of checking a threaded component to ensure that it meets specified dimensional and quality requirements. The following are common methods for inspecting threads:
1. Go/No-Go Gauges: These are simple, mechanical tools that can be used to check the minimum and maximum limits of a thread's major diameter, pitch diameter, and/or lead.
2. Optical Comparator: This is an optical instrument that uses a high-resolution camera to project a magnified image of the thread onto a screen. The image can be compared to a master thread to check for deviations from the specified dimensions.
3. Thread Micrometer: This is a precision micrometer that is specifically designed to measure the thread's major diameter, pitch diameter, and lead.
4. Thread plug gages: These are cylindrical gages with threads cut into them that can be inserted into the threaded component to check the thread's pitch diameter and lead.
5. Coordinate Measuring Machine (CMM): This is a computer-controlled measuring instrument that can be programmed to inspect multiple dimensions of a threaded component, including thread profile, pitch, and lead.
It is important to note that the method used for thread inspection will depend on the type of thread and the level of accuracy required.

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