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Since we are talking plastic mounts vs metal mounts, I decided to take pics of the mounts of most of my lenses. I have more, but they are all metal and show little to no wear at all, mostly just black mars from plastic rear lens caps. One plastic one, I rarely use, doesn't have any wear and isn't pictured. Those in the photos are the ones showing real wear and the most used lenses. The top one fairs the best for the plastics ones, but the top of the first flange is wearing down, though the image is a bit blurry. All the front edges of the flanges are nearly worn round. The 3 other lenses' mounts are worn and/or snapped off due to torsion pressures from not being perfectly the right size to slide into the camera body mount. Over time that snaps them off. Some lenses show gouge marks on the flat section below the flanges. That mark comes from a little metal pin button, on the camera body, that the lens presses when it is put on the camera body. Why its edges are not rounded I'll never know. The bottom lens' metal mounts were pretty much wear free. I decided to test the metal flange by using a knife to scrap at it. It took quite a bit of pressure to peel up that much metal. I feel confident it will never wear or break from normal use, unlike everything else that's plastic.
Another concern with plastic mounts are the rear lens caps and the body caps. Some 3rd party caps will be loose, snug, or too tight. Many people break the plastic mounts off their lenses with those, because for some reason they think they need a full twist to put it on and don't simply snug-tight it gently (reading the reviews will make your IQ drop). Regardless, this comes from manufacturing tolerances being off in some way. Which is why the camera company's caps fit properly and Amazon China's are all wonky as fuck.
Hope this helps.
