A lawnmower uses thin, replaceable blades with a hardened cutting edge and a cross-section defining an airfoil retained in cartridges that are inserted and removed from rotors in a blade assembly at need. The cartridges comprise a blade and rotor interlocking elements affixed to the blade, each rotor interlocking element corresponding to one rotor in the blade assembly. Each rotor and rotor interlocking element includes features that allow the two to be securely engages so that the rotors may be spun quickly in a mower blade assembly to cut grass.