Star Screens can perform 2-fraction screening or 3-fraction screening.
For 2-fraction screening, material flows on top of the stars, that have a predetermined fines size. If the material meets those fines requirements, it will fall between the stars while the larger pieces will stay on top flowing to a discharge conveyor.
3-fraction screening requires two star decks. As the material flows on top of the first deck of stars, mid-size pieces of material fall between the first deck of stars onto a secondary deck with smaller stars. The smaller stars separate the middle fraction material from the fines fraction material. The fines will fall through the smaller stars while the middle fraction material flows to a discharge conveyor.