This arbor less bump knob replaces your worn REEL EASY knob. This fits your RYOBI String Trimmers with REEL-EASY Bump Heads.Simply remove your worn out bump knob and replace with this new bump knob to keep your trimmer head feeding like new. Replacement Part for RY40250, RY40230, P2090, RY41135, RY253SS, RY252CS, RYSST44 & AC04156