A screening belt unit is provided for a harvesting machine or harvested material transportation device and for screening extraneous material out of a mixture of harvested material and extraneous material. A screening belt has at least two endless carriers, preferably in the form of carrier belts or chains, between which screening bars are arranged in a direction transversely to the conveying direction. The screening bars form a plurality of screening bar units that comprise in each case at least two screening bars. At least a part of the screening bars is fixed so as to be movable relative to the endless carriers. The screening belt unit has a positioning means arranged at least locally along the screening belt and acts on the movable screening bars and via which, in the screening zone S as seen in the screening direction, a spacing A in the conveying direction F of successive screening bars is defined. Furthermore, a flap unit, a screening belt and a harvesting machine or a harvested material transportation device are provided.