Abstract: A balance test indexing tool for use in a balance testing machine to assist a user in testing unbalance in a rotor. The tool includes a rotor mount face disposed on the rotor being tested. The rotor mount face may be machined in a surface of the rotor or provided in a separate rotor mount temporarily fixed to the rotor. The tool also includes a rotor mount receiver configured to receive the rotor mount face in the balance testing machine. The rotor mount face and rotor mount receiver are configured to provide an indexing coupling that allows the rotor to be readily indexed to any of a plurality of index positions for unbalance testing in the testing machine. The tool allows multiple balancing runs to be made with relatively little effort needed to re-index the rotor. In some embodiments the tool includes a kinematic coupling that provides highly accurate and repeatable indexing.