Honestly if you are building a 3D printer or any other CNC machine, save yourself the time and effort of continually disassembling and reassembling your machine replacing cheap bearings and just buy these.

Genuine Misumi LMU8 … it is the bearing you need on a Prusa. I should of buy them long ago so he print quality got improved a lot!

Ive built 14 printers with these rails and bearings. The trick is to make sure you prep the bearing right before installing. never slide the bearing over the rail before prep because there can be dirt or debris in the housing that can cause permanent damage to the surfaces. Ive been using break cleaner. Spraying the string of balls at a 45 degree angle will rapidly circulate them bringing any particles out. I then use compressed air to do the same thing to jet out any remaining oil or dirt. be sure to do this in a well ventilated area or wear a P100 mask, break clean and other solvents are extremely harmful to breath in. Pack with them with a pea size dab of super lube or some other silicone based lube. Use 2 rods, one entering each end of the bearing to compress the grease hydraulically forcing the grease into the tracks of the balls, then run the bearing up and down the rod to fully circulate the grease. Wipe away any excess. The result is a silky smooth slide with very minimum lash! There is a small amount of preload and it is very consistent using the more expensive H5 rails. Spend the money, do not use generic rails, you would be wasting a perfectly good engineered to perfection bearing otherwise!

Its INCREDIBLE how quiet my machine is now. I thought it was on stealth mode when i first tried the printer after installing all of these. Just dont forget to clean first with 99% alc for 30 min, then let dry. Then pack them with white lithium grease. I am so impressed with how quiet and nice the printer works now.

Old bearins slid out, new bearings slid in