Use any VEX spur gear as a pinion to drive these rack gears.
Stack multiple rack gears back to back for longer motions.
Combine these with a VEX linear slide and Rack Gear Bracket (sold separately) to create a simple linear actuator.
Each Rack Gear includes (3) 6-32 threaded inserts on their back face. Mount these similar to VEX motors or servos with 6-32 screws.