4 Pcs 2020 CNC 3D Printer Parts European Standard Anodized Linear Rail Aluminum Profile Extrusion for DIY 3D Printer (500mm)

I made an adapter to allow these to mount to traditional 80/20 and very impressed with them now.

The aluminum was as thick as it comes and very strong for a series 20. This is a good buy.

Possibilities I knew when I purchased:There are a few burrs on the ends and metal shavings stuck to the protective layer like others have warned about, I thank them for that as I knew that was a possibility going in. I see some scratches in the paint due to these shavings. I washed these with hot water to get any shavings stuck in the track out, so the paint doesn't look like an issue as one other reviewer has noted.Be careful removing the thin plastic protective layer, use gloves or tweezers of some sort to peel it off.What I didn't know before buying these:If you need exactly 400mm, specify to the seller that you need 400mm or slightly over. The ones I received (4 Pack of 400mm) are not all the same length, and none of them meet the specified 400mm dimension. 399mm or 398. This is due to cuts being out of square and/or improper grinding/sanding of the ends.It doesn't bother me as what I am using them for needs to be cut down to 380mm or can be compensated for in the design process. But the principle of the matter is why they only get 4 stars.What does bother me:When manufacturing a precision product like aluminum extrusions, I feel it's important to account for grinding the ends clean and at least one end being ≈ square, by adding a millimeter or 2 in the cutting process. Generally just giving slightly more than what the customer expects is my motto, certainly not less.I would message the seller if you need = 400mm and not ≈ 400mm to see if they're willing or even capable in delivering on that request or just going with the next size up. I have my doubts about the former, as this is an Amazon Prime Product and is more than likely just sitting in an Amazon warehouse waiting to be plucked from a shelf, cut months in advance.TLDR; Buy the 500mm if you need 400mm extrusions, these are <400mm and not square on any of the 8 ends (whether that is due to an uncalibrated saw blade or grinding/deburring process, who knows). When cutting these down to size, make sure you square an end before pulling your final measurement. If you need this for a 395mm dimension, I would go with the 500mm and deal with being wasteful because squaring the ends you'll more than likely cut off more than what you hope.If Squared ends and length are of no issue, at this point in my review, this is a 5 star product for you.P.S. I will update later if I remember to about longevity, straightness, and overall quality, but the stars can only go down from here as I received a product less than what I expected.

Used it to make modifications/additions to provide more mount points for extruder motors, and electronics. Also gives better options for cable management.

Clean, straight 2020 aluminum. No dents or damage. All consistent correct length too. No complaints.

Very strong parts and high quality.

Finally, something arrives exactly as advertised on Amazon.

Exactly as described