Aoicrie 6 PCS DC Electric Motor 3V-6V Dual Shaft Geared TT Magnetic Gearbox Engine，DIY for Arduino Smart Car Robot Toys Cars Chassis Models Vibration Products (I Shape 1:48 Reduction Ratio)

Hard yellow plastic with white gears made of plastics. It isn’t going to last you ages but for quick projects it will most definitely do the job. It has these squareish mounting mounts with rounded sides which could be used to be attached to other wheels they sell online. Decent torque. Overall not bad.

Exactly what I wanted for a great price. I power a Marble Run machine with mine using a 6v battery pack. With this voltage the output shaft turns about 200 RPM. Great for hobbies of all kinds. You have to solder wires on, but they are reliable and strong.

all the the motors ran great in both directions when tested @ 6V

I am using these to animate a 3D printed marble machine. They seem to turn at about 140 rpm at 3 volts, so they are still a little fast for some projects, but for the price you can’t beat them. The shape akes for easy mounting.

I bought these to power my laser cut marble run machines. These are very strong and did the job.