I have an industrial camera with a C-mount lens, like this one:
(Source of image, last accessed 2022.11.02.)
You can see a tiny screw on the top of the picture. It is used to lock the focus ring or other rings, depending on the actual lens. How can I buy one, if I have lost the one that came originally with the lens?
(Also a longer one would be more useful than those tiny ones that came with the lens.)