CNCTOPBAOS NMRV030 Worm Gear Reducer Speed Ratio 40:1 RV30 NMRV-030 Worm Gearbox Speed Reducer Square Type for Nema23 Stepper Motor/Servo Motor NMRV30 Output Bore/Hole 14mm Shaft

This unit is super solid and is a great price for what you get. Gearbox comes fully lubricated and is factory sealed. so don't expect to open it easily (not that you'd need to). It's full of oil and you'd need to remove the rubber gasket without damaging it somehow. The biggest issue I had was finding the appropriate hardware for driving the input side of the gearbox. The main input has an odd inner diameter of 11mm (7/16") with a 4mm wide key and I underestimated how hard it would be to find appropriate components to drive this with a larger shaft. With that said, the manufacturer included coupler that adapts this down to an 8mm d-shaft and that fits standard sized servos traditionally used for this.

Solidly built, smooth movement with no backlash, but I had to return two of them because the mounting holes for the NEMA 23 motor were on 49 mm centers, not the expected 47 mm (see the photo for the difference)

This was a good quality gearbox and the price was very good. Being used in a prototype to determine life.

I'm using this as a 4th axis on a cnc and need it to be as rigid and repeatable as possible so the lack of wiggle is fantastic

I have been using this worm gear with a stepper motor for a couple of years. It is well made and has been working flawlessly since I bought it. If you need a gear reduction for a stepper motor, I can highly recommend this one.