For the price these are excellent lead screws, dont have to wait to get it from China. Don't ever unscrew the nut from the shaft for any reason, you will lose balls and you will never, ever, ever, ever get them back the way they were. Trust me, videos for repacking ball nuts are for much larger bearings. The balls in these are 2.38 mm, you likely need a custom jig to get this done. Also very important: adding a lead screw can reduce your print quality. The rest of your machine needs to be as precisely aligned as your lead screw is. The acme 8mm rods have plenty of slop to make up for misalignments, lead screw tolerances are much tighter.