Extra stepper motor for the MicroTouch Autofocuser. This motor fits the newer Stellarvue focusers (including the 2.5") that have a 33mm mounting diameter. A smaller size is available for the standard 25mm diameter mounting. To determine which you need, remove both the fine and coarse focus knobs from your Stellarvue scope, and measure the diameter of the steel collar that holds the fine focus bearings.
The stepper motor drives the fine-focus knob on the Stellarvue focuser for the ultimate in precision focusing.