Disclosed is an assembly for a dosing system of a spreader machine for distributing a granular material or the like, which comprises first and second members provided with first and second openings, respectively, and an actuator connected to at least one of the first and second members and configured to provide a driving force between the first and second members, thereby, adjusting an opening size of a dosing opening provided by an overlapping area between the first and second openings, wherein the relative movement is conducted by linear movement of at least one of the first and second members.
