Nema 17 Stepper 5:1 Planetary Reducer
Robot Actuators by LoboCNC
Compact planetary gearbox
https://www.thingiverse.com/thing:2114390
https://www.thingiverse.com/thing:2436716
4:1
NEMA 17 Precision Gearbox with Position Feedback
https://www.thingiverse.com/thing:4440480
6:1
NEMA 17 Robot Actuator by mattiasZ
https://www.thingiverse.com/thing:4428749
Modular planetary gearbox 1024:1
https://www.thingiverse.com/thing:2586962