6Pcs 40mm x10mm DC 5V USB Brushless Cooling Fan, Dual Ball Bearing, Quiet Operation, 4010 Small Computer Fan.

I bought these fans for a small raspberry pi project. They worked perfectly. The USB plug in is great for those who already have a USB use case for them. I spliced the fans in to a 5v power source. The fans are moderate level of noise. All of the fans were functional.

I use these in a project, some of which I sell, so I need the fans to last and I need to be honest with my buyers when I say I've used a ball bearing fan. I've had poor success with fans that use only bushings, some cheap ones have had failure rates as high as 30% within the first few hours of use, even.Despite the listing claiming that these have dual ball bearings, the fans that I got ( which matched the image in the listing ) did not.Since I have been burned before, I ( destructively ) disassembled one of these fans and found oiled bushings inside the fan instead of the advertised ball bearings, which is disappointing.That said, since I destroyed one of the fans, I was unable to return the rest, which was a risk I knew I was taking. I have since used a couple of these in less critical projects where I could easily replace the fan and so far none of them have failed, which is at least better than the previous bushing fans I had.So, I'd say that if you need cheap fans that seem to work, these could be for you, but don't expect them to have ball bearings.