The Bluebird 539007633 Aerator Chain Idler Arm Kit helps maintain proper chain tension and smooth power transfer in compatible lawn aerators. This replacement idler arm kit is designed to support and position the chain idler within the drive system, keeping the chain properly tensioned during operation. It works by allowing the idler to maintain suitable chain tension as the drive sys... https://www.wholetoolbox.com/bluebird-539007633-aerator-chain-idler-arm-kit/539007633.html