Advice from the experts please. I was doing some light pop rivetting yesterday, and as often happens, the retained bit (? shank, ? stem) wouldn't release from the jaws. It's a Stanley hand-operated thing with two jaws. Well, actually it's two of them that both do it sometimes. I got the second because I complained that the first had this problem... as do many others according to a widely-used search engine. I'm now highly skilled at removing the thing (spray oil, mount a nut in a vice and press the jaws down on the nut so that gravity helps the thing drop through the hole in the middle.) But why does it happen and how do you prevent it? Thanks Jonathan