Abstract: A screw press for dewatering sludge and fiber suspensions, having a feed screw, a perforated drum surrounding the feed screw, an inlet or infeed aperture at one end of the drum, and an end wall section at the other end forming an annular outlet or outfeed aperture. The end-wall section includes a plurality of flaps located as an extension of the feed screw, the flaps being yieldably arranged to adjust the size of the outlet aperture. The end of each flap nearest the axis (9) of the feed screw (1) is pivotally mounted on an attachment connection (11), and the attachment connection (11) is arranged for movement along the axis of the feed screw (1). The flaps (7) are arranged to be pressed outwards under the influence of a first force generating arrangement (15,17,18) to form a larger angle with the screw axis (9), thereby causing the outlet aperture to decrease in size.