The Toro 112-9866 Lawn Mower Breather Kit regulates crankcase ventilation for cleaner and more efficient engine operation during use. Designed as a replacement breather kit, it fits compatible Toro lawn mower engines to manage airflow and internal pressure within the engine system. It works by allowing controlled air circulation while filtering excess gases generated during engine operation. This supports smoother engine performance, reduced pressure buildup, improved airflow management, and dependable mower operation during routine lawn maintenance.