What Are These Horseshoe Looking Things?

[wildebeest3]

This looks like a matter best kept between your Spouse, Clergy, Doctor and yourself.

[Juggerknot]

I found it only attracted lightning!

[parkstone bay]

These are Claw Rings, used - typically - on boats with BOOM roller reefing. The claw ring holds the Kicking strap (vang to our cousins), or mainsheet block. The string goes from a swivel on the boom end to prevent the Claw ring from being pulled forward by the kicker.
The boom rotates within the the ring.