Aaaaah... I get it, at last! Thanks MrS. The earlier verbal description makes sense now too - sorry sfgerl for not getting your drift.
I can now happily return to being completely unable to help.
LOL! It's the thought that counts, right?
My apologies for doing such a poor job describing it. After more "googling" I see that it is called the "connecting link", which makes total sense, it connects the remainder of the bracelet to the endlink. And, the two ends are more commonly called either "round", or "wedge shaped". I did find some information that the wedge-shaped connecting link seemed to be used more with the 501B endlink for the GMTs, whereas the round connecting link was more for the 580 endlink and Subs.
I would love to know whether the ("later") wedge-shaped connecting links can be used with 580 endlinks to fit a Sub. Surely, somewhere - this has been tried.
And back to my original question - I am curious to know if there was also a time when the wedge shaped connecting link was "born" - either as a replacement to the round one, or as an alternative-type connecting link.