Hartzell Propeller Inc. does not approve of or endorse any field alterations or modifications to propellers manufactured by Hartzell. Repairs and maintenance procedures documented in Hartzell Propeller Owner's Manuals are the only Hartzell approved practices to be used in the field. Modifications or alterations of a propeller such as counterboring the mounting flange or reindexing the propeller on the engine crankshaft flange may cause a mechanical failure of the propeller. The use of a propeller with an unapproved modification or alteration carries with it a risk of serious injury, death, and/or significant property damage.