Abstract: A concave arrangement is disclosed for a threshing machine such as a combine harvester 10. The arrangement includes a concave 30 having a moveable rear portion 48 that is adapted to vary the break-over angle presented to straw passing downstream. A flap member 54 is provided that moves jointly with the moveable rear portion 48 and ensures that a gap G between the moveable portion 48 and a later processing stage such as a beater apparatus is kept substantially closed. Variation of the break-over angle influences the length of the straw leaving the threshing machine and the loading of the further separation and cleaning mechanisms.