12PCS LM12UU Linear Ball Bearings, 12mm Bore Dia Linear Motion Bushing with Double Side Rubber Seal Great for CNC Machine 3D Printer

Fair price for the quantity (though I only needed half that amount). They appear the same as what's in my Prusa Mk4.

I got these to use in a 3D printer and they work really well for this. I do not think they would stand up to having a large amount of weight placed on them and they come caked in grease or thick oil that gets every where when you take them out of the bag they come in.Originally looking at the image I saw for these they looked like the flat kind of bearing and I had another machine that uses that kind but I must of just saw the top or side view because when they came they were the long roller bearing bushing type. I can still use them but I was hoping for the thin round type and not these.Not sure how well they will hold up because you can see that they are not sealed and the ball bearings inside could come out. I don't really want to have to oil these which these you most definitely will have to for maintenance. I prefer sealed bearings for that reason.

The size is just right for my project. I was able to fit a 6mm rod right through. There is a slight lube on the outer shell. The tube has line etch on both sides in case you need to mount the bearings on the sides. I tried some slightly larger rods. Some of the balls fell out. Maybe I was too rough. Just something to consider if you are planning on putting it under stress. The 6mm means the diameter of the rod that you will be pushing through. I wish they provide all the measurements in the photos such as the outer diameter, the padding in between, and the length of the cylinder. That would save me the trouble of making the measurements myself.