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 at the main pipeline where branching occurs. Four-way tees come in both equal and unequal diameters; equal diameter tees have the same size at the connection ends; unequal diameter tees have the main pipeline connection size the same, but the branch connection size is smaller. A four-way tee is a fitting used at pipeline branch 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 tee. The process involves simultaneous movement and squeezing of the pipe blank by the two horizontal cylinders of the hydraulic press. 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 tube to expand, the metal material flows and expands into the branch tube under the combined action of the side cylinder and the internal pressure of the liquid in the pipe blank.