Hard to say. I see the 'bolthole' - but in full context I see encrustations that resemble normal sea life stuff too - some of it similar to stuff lying about near the same spot, although in less concentration. I also see the end of the 'pin' and realize that it is oddly concentrically round, but I'm still a long way from being able to jump at it being a 'pin' of some sort without more to go on.
The shape of that 'wing root' is interesting - but in scale that would have to be a fairly massive rope or cable lying near / over it, with a fairly massive swage or bead on the rope or cable.
By the way, just a thought, but maybe we should call that rope-thing a 'line' until we know more about what it is. To me it sharply resembles a piece of boat tackle - complete with and end loop whose shape at the end suggests 'memory' (bending) from being loaded against a cleat for a long time, a 'splice' up-line from the loop with that ball swage - which looks like a black plastic 'bead' threaded onto the line... I've knitted a hundred loops like that into marine lines over the years to snag over a cleat - and they tend to take a 'set' just like I see in the end of that one after being loaded. Some people toss old ones overboard after the line gets in bad shape...
One thing that sticks out about all the 'rubble' lying around to me - the area seems clearly disturbed by something: whether 75 years ago or a week before the ROV got there is hard to say, and I'm sure there's plenty of natural rock-fall to do that in the active surf around the reef. But that and the prospective man-made stuff is very interesting for sure, I agree.
Round holes and 'pins' can be a treacherous prospect though - lots of sea critters create amazing shapes too - round 'bore' holes are not uncommon. Can't say so much about the round 'end' on the 'pin' - maybe - but it sure suggests man-made. I love the way you fellas capture these images - it does allow a close look at the details.
LTM -
