Described is a mold jaw half for an apparatus for the production of transversely ribbed tubes, wherein the mold jaw half (16) has end faces and a base face and in its interior a cooling passage with a coolant feed and a coolant discharge, which open at a spacing from each other at the base face of the mold jaw halves. In order to provide a reduced flow resistance for the coolant through the cooling passage and consequently an increased coolant through-put, resulting in an improved cooling action, it is proposed that the coolant feed and the coolant discharge cross, as seen in a direction viewing on to the end faces of the mold jaw halves, and are oriented in opposite relationship with respect to the advance direction of the mold jaw half. That mutually opposite orientation provides that the coolant is virtually shovelled into the cooling passage.