Thanks for the answers, unfortunately they left me somewhat confused, as I can't understand what would be the purpose of control tangs on the shackle. Anyway I went sailing today and also took a photo of the current setup. Anything you would recommend to change?
I've got a J/80 that I bought second hand a couple of years ago and there's one detail that I wonder about. Because the main sheet is attached to the traveler with TWO shackles, connected one after the other. Is this on purpose or some kind of jury rigging? Would it be a good idea to replace them with one?