VEVOR Linear Rail Slide SBR12-1000mm 2 PCS and 4 PCS SBR12UU Slide Blocks Linear Guide Rail and Bearings Kit for Automated Machines DIY Project CNC Router Machines

These two rails came well packaged and undamaged. They are very straight and true.

These are very sturdy rails and though I don't have them up an running yet, I can tell they are going to do well. They are of high quality.

They worked perfectly, Easy to install they came earlier than expected, but yeah very satisfied. I installed the 40 inch rails w/bearing blocks that I bought through Amazon weeks earlier with my router attached to them,so my router system is completer and works smoothly very happy ty

A straight edge laid across the bar shows a deviation of about 1/8 of an inch end to end. I was going to use these for a planer sled as others have done but with the bow in the rail you would get a board thicker in the middle than on the sides. 1/8 " would be a lot of sanding to make the board flat. My old mdf sled which cost next to nothing is a lot flatter. Also the aluminum ends are very roughly cut and protrude out from the round bars, so would have to be filed off if you wanted to put two of these end to end for the table part of a router flattening jig. One of the bearings had some play on the bar but the set screws on the block adjusted the tightness.Update: Contacted Vevor support - extremely helpful and very responsive. Found out that because the difference in the thermal coefficient of expansion between aluminum and steel the bars will distort as the temperature changes ( AL is 2x or more than steel you can visually check this by using a long straight edge and warming the bar/aluminum combo with a hair dryer). They had me loosen the bars from the aluminum and check them again - the distorted one was still distorted even if I removed the aluminum entirely. I sent a picture and Vevor sent me a new bar and it is straight as it should be. Five stars for support, 1 star deduction for sending a bad bar to begin with.For those that are building a cross flattening sled - I was trying to decide whether to use just the bars or the bars with the aluminum extrusion, not knowing how much sag the bars would have with the router and it's carriage. With the aluminum there is no detectable sag, so if you are in a temperature controlled environment then if you loosen and then tighten the bars on the extrusion it will not sag with a router. If, however, you have limited room like I do and setup your flattening system outside then the temperature extremes as far as I can tell could make the bar flex by .5 to 1 mm (depends on what the temperature is and what the temperature was when the bars were tightened). Testing with just the 2 bars ( no aluminum) at full span with a 12lb weight in the middle then the weight appears to make it sag by about .3 mm. Temperature will not affect it. This is with 2 1200mm long, 20mm dia. bars. If the distance is shorter the sag will be less and if the bar diameter is smaller the sag will be more. Obviously if the router/carriage weight is less it will sag less. I am planning on making my sled with just the bars (which would have been cheaper had I known this ahead of time).

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.

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These rails are very nice for the money would recommend to anyone.

Works great for what I needed, though heavier then I thought it would be. Very strong and slides very well