The spool holder is square at the top so each time the extruder pulled in filament, the machine would jerk a bit. This solved that problem.This solved this problem for material spools that are large enough to fit on it (Matter Hackers filament is shown here). The mouse ears are to ensure no warping when using ABS. Just clip them off and super glue the two supports to the bed, and super glue the rounded spool holder to the support plate. Pictures shown to prove that this works. It was printed with the Rostock Max V2 I just finished building.