Well, I'm used to shackles for connecting halyards to sails and shackles to connect anchors to chain and anchor line. There are tack shackles, stamped shackles, snap shackles, headboard shackles, etc.
So what's the difference? As far as I can see, each is designed to take the load for its designed use. And if you're using a shackle to connect parts of an anchor rode together, as mentioned above the anchor chain and rope will not always be in a straight line. So the bow/anchor shackle has a bow in it to allow misalignment.
You can get anchor/bow in either stainless or galvanized. but the galvanized will have a painted steel pin.
Was that the question?
Boris