These power rack & pinions fit the majority of Rayburn, Mastersbilt, Barry Wright, Rocket (blue), Victory Circle and Warrior chassis and are 18-1/4".
Rack speed is measured in inches per turn. If you turn the pinion (1) time, the rack shaft will move between 1-3/4" (slow) and 3-1/4" (fast). That number is stamped on the front of the housing next to the greases fitting.