Four-way tees are used for pipe fittings and pipe connections. Also known as four-way pipe fittings or four-way tees, they are used where the main pipeline branches off. Four-way tees come in both equal and unequal sizes; equal-size four-way tees have ends of the same dimension; unequal-size four-way tees have the main pipeline ends of the same size, but the branch pipeline ends are smaller. Four-way tees are pipe fittings used at pipeline branching points. The hydraulic expansion forming process of a four-way tee involves using a hydraulic press to inject liquid into a pipe blank of the same diameter as the four-way tee. The process uses the two horizontal cylinders of the hydraulic press to synchronize movement and compress the pipe blank. As the pipe blank is compressed, its volume decreases, causing the liquid inside to increase in pressure. When the pressure reaches the required level for the branch pipe to expand, the metal material expands into the branch pipe under the combined action of the pressure from the side cylinders and the liquid inside the pipe blank.