Imagine a set of helical pairs whose fixed nuts are tightly fitted over the periphery of Flat Washer BS . When the screw is twisted, the screw rotates along the thread as the fixed nut, Through the nut, the whole movement is called "screw motion". The helical mechanism transforms the rotational motion into a linear motion, transforming the torque into a straight line force. By means of this mechanism of force, the force can be amplified and a smaller rotational force (torque) applied to the shaft can be transformed into a larger axial force. The pitch is the axial distance between two adjacent threads. The smaller the pitch, the greater the mechanical benefit, ie the greater the ratio of the output force to the input force. For threads that do not allow transitional buckle or undercutting, the traditional turning method or tap is used, and the die is difficult to process, but it is very easy to use CNC milling. In addition, the durability of the thread cutter is ten times or even several times the tap, and in the process of CNC milling thread, the adjustment of the thread diameter size is very convenient, which is the use of tap, the board is difficult to do. Due to the many advantages of thread milling, the current high-volume thread production in developed countries has adopted the milling process more widely. Some machines that use helical mechanisms do not necessarily have shafts or threads. For example, the Archimedes type spiral pump is a water pump that rotates around the axis of rotation by a helical surface, passing water from a low point to a height, and the plug is a sharp, spiral-shaped, The handle will cause the thick wire to be drilled into the vial of the veneer. Apply a screw mechanism, the screw can be screwed through the fixed nuts. For example, hardening the wood screw can cause it to drill into the wood. In turn, the nut can be screwed through the fixed screw. Flat Washer BS -