A liquid-cooled heat sink for use in combination with a heat exchanger to cool electronic or electrical devices attached to said heat sink comprises a metal block having a plurality of circular passageways therethrough defined by cylindrical walls. An inlet is in fluid communication with one end of the passageways for receiving a cooling liquid, and an outlet is in fluid communication with an opposite end of the passageways for outputting the cooling liquid. At least one tape insert is mounted within at least one of the circular passageways, wherein the tape insert longitudinally bisects the circular passageway and further wherein edges of the tape insert abut cylindrical wall.