Raymarine M81138 Universal I/O Linear Drive Stern Drive Autopilot A12012 N018Raymarine M81138 Universal I O Short Linear Drive Sterndrive Autopilot Autohelm Raytheon A12012 N018 M81138 Professionally refurbished with full warranty. Refer to the photos for exact dimensions. It is designed to drive cable operated, power assisted steering systems. It operates the power steering valve in the same way as the steering cable. When you disengage the autopilot, a clutch disengages the I O drive so you can steer the boat manually.