A cooling system for the cooling of tool pieces (1) is disclosed, operating by means of a cooling fluid running from a fluid inlet (2) to a fluid outlet (3) through connecting lines (7, 8), whereby the tool pieces (1) are connected with a through flow to at least one connector line (7, 8) connected to the fluid inlet (2) and at least one other connected to the fluid outlet (3). According to the invention, other tool pieces can also be cooled outside sleeves forming cavities with high efficiency and increase in fluid turbulence, whereby at least one additional connector line (10 - 12) is connected between the at least one connector line (7) connected to the fluid inlet (2) and the at least one connector line (8) connected to the fluid outlet (3) in fluid connection therewith, connected therein such that the fluid flows serially through at least two tool pieces (1) in the fluid path thereof.