Many people make mistakes when mounting servos that can lead to servo damage, premature servo failure, or other problems. When installing the servos the brass eyelets install from the bottom of the rubber grommet, and then the screw is tightened to where it just touches the top of the rubber grommet. The purpose of the rubber grommet is to isolate the servo from the vibration in the airframe during flight. If the screw is over tightened to the point that the rubber grommet is compressed any the isolation characteristics of the grommet are gone and vibrations will travel directly into the servo, which can damage it.

See attached diagram

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