I received 2 packs to inexpensively size my CNC router to the right size. They are. Work. I think. One of the clutches I received from 4 was the wrong size. I needed 10mm x 8mm connectors and this one was 8 -> 8. I probably should have returned the part at that precise moment but for some reason I didn't. In my (weak) defense, my budget was too high, which is a rookie mistake with this type of project because they are black holes of money, time, and sanity. I tried drilling the wrong coupler to the right size. but of course they are pure distilled chinese and it's basically exploded. The 3 on the CNC router seem to work fine, but I'm willing to bet they'll break pretty easily if I smash them too hard. Anyway, I wouldn't buy them again. Zero quality control and they are fragile. But they are probably suitable for building a 3D printer.