Four-way fittings are used for pipe joints and pipeline connectors. Also known as four-way pipe fittings or four-way connectors, they are employed where a main pipeline needs to branch off. Four-way fittings come in both equal and unequal sizes; equal-sized four-way fittings have all branches with the same diameter; unequal-sized four-way fittings have the main pipeline branches with the same size, while the branch pipeline connections are smaller than the main pipeline ones. Four-way fittings are a type of pipe fitting used at pipeline branching points. The hydraulic expansion forming process of a four-way fitting involves using metal material's axial compensation to expand the branch pipe. The process involves using a hydraulic press to inject fluid into a pipe blank of the same diameter as the four-way fitting, then synchronously moving the two horizontal cylinders of the hydraulic press to squeeze the pipe blank. As the pipe blank is compressed, its volume decreases, causing the fluid inside to increase in pressure. When the pressure reaches the required level for expanding the branch pipe of the four-way fitting, the metal material flows and expands into the branch pipe under the combined action of the pressure in the side cylinder and the fluid pressure inside the pipe blank.