We're not in the Navy, and D rings seems to be the more common term. The primary definition of shackle is a device used to restrain a prisoner.
I've never had this happen. The ones I use have rubber washers and isolators to prevent rattles. I mount the D ring, put a screwdriver through the hole in the pin and crank it down. Vibrating loose is possible, I suppose. If I ever have one loosen, I'll put some LockTite on it.
Go ahead. We all have our things. It makes me nuts when people refer to wheels as rims. A rim is a part of a wheel, but it is never a wheel. Or referring to a magazine as a clip. They're two completely different things. Or "Nos". NOS is Nitrous Oxide Systems. It's a brand, not a chemical. The chemical is Nitrous Oxide, Nitrous, or N2O. Shall I go on?