The Toro 117-5299 Lawn Mower Idler Pulley maintains belt tension and alignment in compatible mower systems. This pulley mounts on an idler arm and rotates as the belt moves during operation. It works by applying controlled pressure against the belt, keeping it properly positioned on the pulleys and preventing slipping. Smooth rotation supports consistent power transfer. Replacing a worn pulley restores proper belt tracking and steady mower performance.