12 Pcs LM8UU Linear Ball Bearings, 8mm Bore Dia, 15mm OD, 24mm Length with Double Side Rubber Seal Great for CNC, 3D Printer

Had a musimi bearing go bad within a month. Prusa is sending me more, but I wanted to get the printer back up and running and one of these bearings is working fantastic so far. They are cheaper than musimi, even being carefull I destroyed one by knocking out 4 balls without feeling them come out, so be very careful when packing grease and putting onto the rod. Second one went on without a hitch and is completely silent 2hrs into a 18 hour print. Works fine as a stopgap until the official ones arrive. glad to have spares too.

These bearings are a perfect replacement for those on my MK4S. I will purchase again, if needed. Recommend you do the same.

Easy replacement for my Prusa i3 Mk3.

Not top quality but could not find better - we will see how long they last before the balls depress into the nylon housing -

EDIT: Perhaps I received a really, really bad batch. Been trying to get them run smoothly without success. Sorry, needed to deduct a couple of stars, it was a waste of money. They're noisy, balls fall out and don't run smooth! Not one does the job. --------------------------------------------- Yeah, not smooth. I found 3 out of 12 that are somewhat usable. To me it seems the balls aren't exactly spherically, perhaps they haven't found a way to make them round and still make a profit? I have packed them with grease coming out of their ears. Yet, there are rough spots, which is not acceptable and points to the ball. This would introduce ringing, well not really ringing. When it hits a rough spot, the stepper motor has to overcome that resistance, which may cause a slow down of the print head for example. Kinda like a vehicle that does brake in short successions. Most of us don't like that forward / backward motion, either. It would leave artifacts on the printed object. That's why 3D printer manufacturer often opt to use a aluminum extruded bar, with wheel carrier (print head or "Y" carriage) that is far less expensive than high quality linear bearings. On some, I noticed a smoother ride once I turned the bearing axial. That would actually mean the the bearing ferrule is ever so slight oval. Over time they may work better but would wear out the rod, however there is no way that they will work out of the box / bag. The ones that work smoother, have possibly a larger tolerance and don't ride on all balls. For those that can afford it, get high quality linear bearings from Misumi or other known manufacturer with high quality standards. You may get only one or two bearings at the same price tag of the 12 included in this package. The quality standard for the reviewed is rather low!

Works great

The bearings are well built, the rubber end seals look to be nice and clean. I neglected to grease them before first use on my 3D printer, so they did start grinding after a little use. I removed, cleaned, and greased them and they work great. Very smooth and quiet action.

I bought these to replace a few worn-out bearings on my Prusa i3 MK 2.5 printer. Thankfully, I only needed a couple, since these bearings are very inconsistent. Out of the 12 I received: 1 felt tight and ran rough on the smooth rod. 4 felt very loose and had considerable play. 7 were of passable quality--they moved smoothly but still had a bit of play. I tested these on a brand-new linear rod and made sure to roll them back and forth to break them in. For reference, I also tested several original bearings from my printer, and they fit almost perfectly with virtually no play, which should rule out tolerance issues with the rod. I installed these bearings as a temporary fix to get my printer up and running again. I only needed to replace some Y- and Z-axis bearings, so it's a good thing I didn't need all 12. I packed them with grease for good measure. After getting everything put back together, I immediately noticed that the axes I replaced bearings on were considerably louder than before. In addition, I could hear rattling when the printer made certain movements. I also noticed that the print bed wobbled a bit more than before, possibly due to increased bearing play. It was an acceptable amount (barely visible, but I could hear clicking when I pushed it back and forth) but more than I remembered with the stock Prusa bearings. Despite all this, I haven't noticed any major differences in print quality. Perhaps more precise prints will show a difference, but performance is acceptable for my purposes. These bearings (at least the ones that worked) will probably be fine for the time being. However, it is disappointing that only a little over half the bearings in a pack of 12 are usable.