The present disclosure refers to an assembly (10) for a dosing system (3) of a spreader machine for distributing a granular material or the like, comprising: a first member (11, 12) provided with a first opening (17, 18), a second member (11, 12) provided with a second opening (17, 18), and an actuator (20) connected to at least one of the first and second members (11) and configured to provide a driving force for relative movement between the first and second members (11), thereby, adjusting an opening (17, 18) size of a dosing opening (19) provided by an overlapping area (16) in which the first and second openings (17) are overlapping. The first and second members (11) are moveable by the relative movement into a first position providing the dosing opening (19) with a first opening (17, 18) size and a second position different from the first position and providing the dosing opening (19) with a second opening (17, 18) size different from the first opening (17, 18) size, wherein a center portion of the dosing opening (19) is locally fixed when the first and second members (11) are moved between first and second positions. Further, a dosing system (3) for a spreader machine for distributing a granular material or the like comprising the assembly (10) is provided. A spreader machine for distributing a granular material or the like is provided.
