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 of the same size, with the branch pipeline outlet being smaller. Four-way fittings are a type of pipe fitting used at pipeline branch points. The hydraulic expansion process for four-way fittings involves using a hydraulic press to inject liquid into a pipe blank of the same diameter as the four-way fitting. The press's two horizontal cylinders synchronize to move and compress the pipe blank, causing it to shrink in volume. As the volume of the pipe blank decreases, the pressure inside the liquid increases. When the pressure reaches the level required to expand the branch pipe of the four-way fitting, the metal material flows and expands into the branch pipe under the combined forces of the side cylinder and the internal pressure of the liquid in the pipe blank.