One of the four motor does not work.
I have to request Amazon to send me another set so I can get four working motors.

Does not handle viscous materials well, but a good little pump for all other liquids.

Not super great with unclean water, gums up eventually if there's too much cleaning solution in the water

I bought this pack of 4 mini submersible water pumps for my husband who is always building things, doing projects. My package arrived within 2 days. 2 of the pumps worked, the other 2 did not. For the price I paid I am not upset over the fact 2 didn't work. Stuff happens. I contacted the seller and they promptly got back in touch with me. Let me know they have shipped me another pack of 4 pumps. The 2 pumps that are working, work great as they should. I have no complaints. I would recommend these to anyone. I would definitely buy again!

For some small automation or school project these are a bang for your buck. The dimension schematics and specifications are in the product images and description respectively so you can have a solid idea if they will be useful for the intended use. I used mine to automate the watering of some potted plants with an Arduino. As noted in another review the wires are very thin and depending on the usage it would be better to solder thicker (image) ones. Also there is a gap at the top between the wires and the case, so water might get in. These are definitely NOT submersible as there is a space near the bottom over the output tube where water might get in. The seller also discourages continuous usage so if your application demands that find something else. Overall these are great $3.25 pumps.