I recently bought a stereo microscope head and needed a stand for it. The best stands are double arm boom stands, which use two linear rails. I have a 3D printer, so I figured, why not just build one? Looking at McMaster-Carr, linear rails and pillow blocks are EXPENSIVE. I looked elsewhere online, and they still weren't anywhere near what I wanted to pay. So then, of course, I checked Amazon and found these. I probably could have gotten away with the 16mm rails for my application, but I decided on the 20mm x 1m. First of all, they're super heavy. I guess that should be expected. They have a nice coating of oil on them, which seems to get on everything like anti-seize does - nothing a little brake cleaner can't take care of. The rails are straight and have a nice polish, and they measure 20mm +0.1/-0.2. The ends aren't chamfered, which would have been preferable, but that's an easy fix. The pillow blocks seem well made, with recirculating ball type bearings in them. Putting the two together, the blocks slide nicely on the rails, though they're a bit loud. The dust seals on the blocks seem to be well-fitted and there's no discernible play in the bearings. I need to cut these rails down, and I did so using an angle grinder with a cutoff wheel. I then polished and chamfered the ends with a 120 grit flap disc. Cutting took a couple of minutes per cut. You could probably do it with a hacksaw but it'll take you all afternoon. Out of curiosity, I tried drilling into a piece of the rail and I was able to drill without too much problem, so the rails aren't too terribly hard. Overall, these are a great choice if you need a set of linear rails, pillow blocks, and mounting blocks. I'll be posting my build to Hackaday and thingivese, and I'll be recommending these rails to anyone looking to build their own microscope stand.
Davy M Hay 
