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I don't have any good book references at hand, but here is my guess.

Below, 3 pics. With arrows pointing to what I am assuming you are asking about.

One looks to have maybe a degaussing cable attached to it? Or just a safety line?
Another looks like it's holding a boat?
And yet another is unused when there are many ropes hanging down around it.

So, my guess, a generic tiebar. Used when needed.

And FWIW, they were there before the blister was added.