The pipe connections have different diameters. Reducing diameter, and what kind of, and their specific is how to distinguish, I'm a novice, seek expert advice
Six links, or even moreAccording to material classification, same material, different material
According to the form of joints: pipe plug, two - way connector, three - way connector, four - way connector,
If there is no change in diameter: different diameter (that is, variable diameter) joints and the same diameter joints
