The screws on my Cartel EX target sight (and everything else on my bow, for that matter) are always coming loose. I managed to lose the brass windage adjustment thumbscrew today. I’m not sure on the exact specification of it, but the thumbscrew from a VGA, DVI or other D style connector is the same thread. A handy replacement!
While I was at it, I checked the elevation adjustment, and it is a M5x0.9 thread, which is the same as the two 3mm allen head bolts holding the vertical rail/scale to the extension bar. Can’t imagine this one would be easy to lose though as your sights would drop if it came loose.