Thread introduction
Thread refers to a continuous convex portion of a spiral shape with a specific cross section made on the surface of a cylindrical or conical body. Threads are divided into cylindrical threads and conical threads according to the shape of the mother body; external threads and internal threads are divided according to the position of the mother body; triangle threads, rectangular threads, trapezoidal threads, and zigzag threads are divided according to the cross-sectional shape (dental shape) And other special shape threads.