An eccentric screw machine (10) demonstrates a Stator (11) having an inner lining (17), which demonstrates teeth projecting inwards. The tips of these teeth are provided with micro-ribs (26 to 29), which are embodied asymmetrically with respect to the radials (R). They preferably demonstrate a flatly rising edge (30) and a steeply falling edge (31). This thus results in improved operating performance, depending on the direction of rotation.