This sleeve positions and retains the chopper knife on its mounting shaft within the straw chopper assembly. It acts as a spacer between the knife and the shaft shoulder, maintaining the correct lateral alignment of the cutting edge relative to the counter-knife. A worn or deformed sleeve allows the knife to shift, causing uneven wear on the blade and reduced chopping consistency. The manufacturer machines this sleeve to the same inner and outer diameter tolerances as the original component, so the knife fits without additional shimming.