I wonder if this has ever happened in actual use.... Some 35mm bodies are made of metal, either brass or in more recent years magnesium alloys. Some are made out of poly-carbonate (ie. plastic). Some of my lenses are quite heavy, such as 70-200 f/2.8 VRII. If it is on a tripod, the tripod is mounted to the lens not the camera. But I hand-hold these a lot, that means when not in use, they hang off of a camera body which in turn has a strap which hangs from my shoulder. Does the lens mount ever break as a result of weight or momentum? I can see how it can break if there is an impact, but that's not what I'm thinking about. In usual and common use, the combination hanging from shoulder and gently swinging, would it?