An insertion piece to a single-grip mixing faucet developed as a control unit. On one side, the control unit is connected to a footing having warm and cold water inlets. On the other side, the control unit is connected to a driving arm. The control unit includes a fixed inlet disc and a moving control disc arranged above the inlet disc to form together a plane sealing. The side of the inlet disc opposite the control disc is coupled to the footing, whereas the side of the control disc opposite the inlet disc is in connection with a ceramic moving element, which, in turn, is in connection with the driving arm. The inlet disc includes at least one inlet opening for warm water, at least one inlet opening for cold water, and an outlet hole forming at least two outlet openings, preferably one for tub filling and one for shower filling. The driving arm independently controls the separate outlets.