A screw assembly for a triple screw pump includes a central screw and at least one lateral screw, both provided with one or more helicoidal threads. The lateral screw is arranged to mesh with the central screw, with a lateral screw axis being parallel to a central screw axis. The distance between the axes of the central screw and the lateral screw is greater than the half and lower than 3/5 of a central screw external diameter.