A threshing and separating system includes a concave； a shaft defining an axis of rotation which is parallel to the concave and transverse to a longitudinal axis； and a plurality of slats rotated by the shaft and configured to move crop material against the concave. The slats have a helical shape winding around the axis of rotation. The slats include a first set of slats being predominantly on a left side of the shaft and having a left-handed helical shape, and a second set of slats being predominantly on a right side of the shaft and having a right-handed helical shape. At least one slat of said first set of slats is staggered relative to a closest slat of said second set of slats, such that a portion of a slat length of said at least one slat is overlapped with one or more adjacent slats of said second set.
