Purchased January 2021. I only needed two but was glad there were 4 at the time because a pair broke trying to install. The other went in well, although it seemed a bit stiff. Well, in June we noticed that a strip of ball bearings (built into a strip of plastic) had actually fallen out. The box was still working, but then we noticed loose ball bearings and by August it was completely out of order. And all this with easy handling and low weight (much less than calculated). I should also note that after the failure I just replaced the Knape and Vogt sliders which are MUCH higher quality to begin with. a bit more money - strong steel for bearing holders etc. It's also a lot easier to install and still works great - no stiffness and a fantastic soft close (much more so than these have ever worked).
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