3x8x4 mm Miniature Steel Bearing Skateboard Deep Groove Ball Bearings Pack of 10

If anyone is wondering, these 3x8x4 mm bearings are the correct size for the Bambulab extruder gear. They fit perfectly and work smoothly without any issues. A great value pack for anyone needing replacements or spares!

Good Bearings, Smooth and Clean, good tolerances. I highly recommend them.

In short these aren't top quality but they are pretty good, especially for the price.I bought these for yoyo's. For those who don't know, modern unresponsive yoyos require very good bearings to perform correctly. These are a size D in yoyo terms. I think these will work well for any high speed application, within reason. The spin is nice and there isn't much slop. The metal looks good quality and is machined nicely. I can't say for sure but I think it has a metal cage too(junk bearings use plastic). I think they would be fine for rc as well. My main issue is the shielding cannot be removed and they come with a bit of grease. The grease in these is not too bad compared to others but I would have preferred a light oil or dry over the grease. I knew the shielding wasn't removable before buying and others in this size with the removable stuff have been bad for me so be careful with that. I have had bought plenty of terrible bearings that are garbage and it is hard to gauge quality from listings. That's why I made a review to help others. In summery, I like these and I think you will too.

I recently purchased these to replace some bearings in my UK Arms M249 gearbox on the cheap. I was highly satisfied with them considering they matched the dimensions listed and all spun freely with no issues after using them for about an hour. I also like how they are sealed on both sides versus the previous one's I had that were susceptible to getting gunked with dirt, metal fragments, etc. Exactly what I needed for a great price.

These have very good performance as wind speed sensor bearings and two of them stacked work well for wind vanes (the addition stiction dampens wild movements).I use them with these screws and nutsnuts: https://www.amazon.com/gp/product/B07XNLD2J5/screws: https://www.amazon.com/dp/B09Y5QYK6LI make bearing bosses from 10mm thick disks I cut from 1” dia delrin rods. I bore the bearing bosses using an “O” size bit, for a 1 bearing boss I drill about 4mm deep and for a 2 bearing boss it’s about 8mm deep. Those disks then screw onto 1/2” pvc furniture caps with holes drilled in the center. Magnets are affixed to the head of the screws and protrude into the 1/2” pvc pipe.

Sadly I bought the wrong size. I needed 4mm tall bearings and accidentally ordered 5mm tall bearings so I had to return and reorder. I'm sure these are well made decent bearings so long as your not looking for top preformance abec7 or 9 bearings.

2 were bad out of the gate, and all of them are fairly noisy in the brushlless motors I put these in.

They seem to be working fantastic so far. Measurements were precise. Bearings nice and smooth. We will see how they work over time. FYI I used these to replace bearings on a race drone.