I ordered some LM4UU linear bearings for a project I'm working on at work. They arrived within a few days (well packed I would say) in the mail. I tested them out on a 4mm rod and it feels like they're locked up. I tried to move them back and forth enough to get the lubricant moving, but no luck -- they might as well not even be bearings. I don't know if I got a bad batch or what, but they are nowhere near as low friction as the LM8UU bearings they were intended to replace in the process of miniaturizing the design.