The only thing that I can complain about was the ups driver who threw the package on the floor sounded like something fell off the roof into my building .I just got to first floor as he was walking out with his cell phone at he ear !
I used these for making a sliding table saw. They take a little time to get set up just right but it’s worth effort. I know that there are better and more expensive rails out there but for the table saw they were just fine.
Very smooth. Rail appears to be case hardened, not through hardened, but I could be wrong about this. Very little play on bearings. I cut to size and used to increase rigidity on a 3018 CNC.