...metal ring (cylinder with no top and bottom), that is used in combination with connecting elements. It is put directly on the pipe underneath the coupling. After the fitting is connected and pressed against the tube ferrules are squeezed, and they assume the shape of the inner room between a connection element and a pipe. It provides additional protection from any damage, ensures tight and leakproof connection. A ferrule is a very useful component and is always used to provide a complete and uncompromised bond of the pipes and prevent any loss of transported substances.