The Toro 139-7915 Lawn Mower Idler Arm Assembly helps maintain proper belt tension for reliable mower operation. It works by supporting the idler pulley and allowing it to move as needed to apply and maintain tension on the drive belt. This helps ensure consistent belt engagement and smooth power transfer to the mower's operating components. Replacing a worn, bent, or damaged idler ar... https://www.wholetoolbox.com/toro-139-7915-lawn-mower-idler-arm-assembly/139-7915.html