Milwaukee's 21" Mower Blade is designed for use with Milwaukee's M18 FUEL? 21" Self-Propelled Dual Battery Mower (2823-20). The 21" lawn mower blade is a direct replacement for the blade kitted with MILWAUKEE? M18 FUEL? 21" Self-Propelled Dual Battery Mower. The steel blade offers you increased durability and longer life. The precision-machined cutting edge delivers an improved cut quality.