Abstract: A material grinding tube mill having a composite diaphragm (5) at the outlet end of a grinding chamber (3). The diaphragm comprises a coarse grate (6) facing the grinding chamber (3) for retaining grinding bodies in the chamber (3), and, on the side of the grate (6) remote from the chamber, a sieving screen (7) for sieving the ground product. The coarse grate has a plurality of openings (20) which constitute substantially the effective open area of the coarse grate. Disposed within the space defined between the coarse grate (6) and the sieving screen (7) are guiding members (21, 22) to guide coarse particles backwards to the grinding chamber (3) through one or more apertures (19) in the coarse grate (6) which allows free passage of the coarse particles.