14.4 : 1 reduction ratio M5 nut fixture 0.8mm/turn ou will need an M5 hexagonal head screw, at least 70 mm long. since the control of the speed is very accurate the distances are arbitrary but the math needs to be done EDIT: This worm gear was designed to fit a home made star tracker, made up of two hinged boards. The stepper motor was the way to go due to its very high precision in rotation and using micro-stepping, the ride is smoooth. Plus, you get huge torque (not that it's really needed, but hey, it was the smallest i had). As the point of the gear is to spin a nut along a long-enough screw (M5) the screw needs to not rotate, thus the role of the "hinge" Pictures will be posted upon completion. A video of the entire assembly in action soon to come.