Gear drive systems used with a camera comprise a housing with an electric drive gear disposed outside of the housing. A host gear is engaged with the drive gear and is rotatably disposed on a stationary shaft extending from the housing. An adapter is attached to the host gear and extends axially outwardly therefrom. A secondary gear is attached to the adapter and comprises a plurality of teeth disposed along an outside diameter. The secondary gear is releasably attached to the adapter by retaining elements and is fixed rotatably to the adapter by registration elements. The secondary gear is attached to the adapter by a push on snap-fit, and is removed from the adapter by being pulled off, thereby avoiding the need for tools to interchange a secondary gear having a desired configuration of teeth to engage a camera optical adjustment element such as a lens ring.