Threaded connection is a widely used detachable fixed connection, which has the advantages of simple structure, reliable connection, and convenient assembly and disassembly. The traditional thread detection method is to use a thread gauge for contact or a universal tool microscope for manual measurement. The workload is large, the work efficiency is low, and the measurement results are easily affected by humans.

According to the shape of the plane figure, threads can be divided into triangular, rectangular, trapezoidal and zigzag threads. According to the winding direction of the helix, it can be divided into left-hand thread and right-hand thread. It is stipulated that when the thread is upright, the helix rises to the right into a right-hand thread, and rises to the left into a left-hand thread. Right-handed threads are generally used in mechanical manufacturing, and left-handed threads are only used when there are special requirements. According to the number of spirals, it can be divided into single thread and equidistant multi-thread threads. For manufacturing convenience, the thread generally does not exceed 4 threads.