Overall good product. They roll smoother than the other rails I got from ebay. Do not expect perfection at this price. But they are "good enough". Make sure you back out the adjustment screws before trying to install the carriages on the rail. Also you will probably want to order some ball nut housings as they are not included. Don't forget to grease the carriages before installing them, and "run them in" a little bit (slide back and forth on the rail for a while) and the smoothness will increase.One problem with all cheap ball screws I have found is the BF (floating end) is often just a tiny bit too large to fit into the BF block. You can try heating the BF block and cooling the end of the ballscrew to get them assembled, but if you do this they will be nearly permanently stuck together and hard to take apart once the temp equalizes. Instead of doing this I just took some 1000 grit wet-dry sandpaper, wetted it with WD40, and used a cordless drill to spin the ballscrew while I held the sandpaper around the BF end of the ballscrew. The grit is so fine it does not remove much material, it more polishes off the microscopic burrs than anything. Spin only a few seconds then test fit to see if it can slide into the BF block. Easy peasy. Not going to deduct any stars because I would rather have them a tiny bit too tight than too loose, and it is easy to fix.