I could be wrong, but I believe that pin you see in the left photo is where you plug a cable that the other end would plug into your camera. This would have allowed you to take your flash off camera. (Today this is done wireless)
Do a search for sync cords. You'll see examples of them.
I have an F-1 as well and thought it may be for it, but I thought that the F-1s had shoes attached to the replaceable viewfinders. My F-1 does not have a hot shoe which is why I was thinking in that direction.I was thinking the same thing, that it's probably a hot shoe for earlier cameras that didn't have a hot shoe. I don't think I have a Canon early enough to not have one but have a Konica that's from maybe the '60's that doesn't have a hot shoe.
You could look up the virtual Canon Museum.
And happened to think, I do have an F1 that was a 'pro' level SLR that doesn't have a hot shoe. I think SLR's by then usually had them but being a camera intended for pros they would have been less likely to use an onboard camera flash.
Ok, I must have missed them. I must have not been using the right key words, just kept seeing hundreds of other shoe adapters. That makes total sense, I was going to check out my F1 again, but have a bad back at the moment and hadn't gotten a chance yet. Thank you very much for your input!There are several ads on ebay listing an item identical to yours and they are all described as hot shoe flash adapter for Canon F1.