Four-way fittings are used for pipe joints and pipe connections. Also known as four-way pipe fittings or four-way joints, they are employed where the main pipeline needs to branch off. Four-way fittings come in both equal and unequal sizes; equal-sized four-way fittings have all outlet ends of the same dimension; whereas, unequal-sized four-way fittings have the main pipeline outlet with the same size, but the branch pipeline outlets are smaller. Four-way fittings are a type of pipe fitting used at pipeline branch points. The hydraulic expansion forming process of a four-way fitting involves using a hydraulic press to inject liquid into a pipe blank of the same diameter as the four-way fitting. The hydraulic press's two horizontal cylinders synchronize to move and compress the pipe blank. As the pipe blank is compressed, its volume decreases, and the liquid inside increases in pressure. When the pressure reaches the required level for the branch pipe to expand, the metal material flows and expands into the branch pipe under the combined pressure of the side cylinder and the liquid pressure inside the pipe blank.