MST small angle head in Japan, also known as small 90 degree right angle milling head or machining center angle head and NC angle head, is a kind of machine tool accessory. After the milling head is installed on the machine tool, the tool rotation center line can process the workpiece at an angle with the spindle rotation center line. Originating in Europe, it has been widely used in various fields of machining such as aviation, automobile and mould. Using the milling head can increase its processing range and adaptability without changing the structure of the machine tool, realize some processing that is difficult to complete by traditional methods, reduce the repeated clamping of workpieces, and improve the processing accuracy and efficiency. It is mainly used in machining centers and gantry milling machines, in which the light can be installed in the tool magazine and can be freely converted between the tool magazine and the machine tool spindle; Medium and heavy-duty have high rigidity and torque, which can be applied to most processing requirements. Because the milling head expands the service performance of the machine tool, it is equivalent to adding a shaft to the machine tool. It is even more practical than the fourth shaft when some large workpieces are not easy to turn over or high precision requirements.