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.
Great linear brakes! 
