Abstract: A device for centering a rotational unit on a rotatable hub for rotation of the unit together with the hub. A centering surface which extends around the circumference of the hub extends essentially from a mounting edge for the rotational unit to a stop surface which determines the axial position of the rotational unit. The rotational unit presents in a corresponding way a centering surface which in its one end transcends into a stop surface, which determines the radial position and which is intended for contact with the stop surface of the hub. One of the centering surfaces is divided into a first centering section with a certain larger clearance to the second centering surface and a second centering section with a certain smaller clearance to the second centering surface. The first centering section extends across the main part of the axial distance from the stop surface of the hub to its mounting edge.