Associated brand optional Modified Rotor for the Sonic540 Brushless Motors. F...Associated brand optional Modified Rotor for the Sonic 540 Brushless Motors. FEATURES: Increases torque for applications such as 4WD buggies and touring cars YOU WILL RECEIVE: 13.0 x 25.3 (5.0) Modified Rotor jxs 09/10/12 ir/jxsmore