Part for connecting pipe to pipe. According to the connection method can be divided into socket pipe fittings, threaded pipe fittings, flange fittings and welding pipe fittings four categories. To make more of the same material as the pipe. Elbow (elbow), flange, three pipe and four pipe (crosshead) and reducer (reducer) etc.. Elbow for the turning of the tube; flange for tube and pipe connected parts, connected to the pipe end, the three-way pipe for three root tube collection place; four-way pipe for four pipe collection place, different diameter pipe for connecting the two pipes with different diameters.