Abstract: A positive-displacement pump, in particular for use in machines or dispensing fluids, including two elements that are with respect to one another and which mesh with one another (20, 30), each of them being rotatably mounted in the pump with centered coupling without interference with a corresponding centering body (18, 11a). At least one of the two above-mentioned ratable elements has a plurality of undercut regions (26, 34, 35)) at the location of the centering walls. The undercut regions (26, 34, 35) comprise a wall portion which is spaced with respect to the facing wall of the respective centering body.