I have a series of rings secured to a boom. Their function is to keep the mainsheet from flopping around.
There is little or no stress on the rings, and minimal forces trying to slide them back-and-forth on the boom.
I'm throwing a clove hitch around the boom, tying it off with a square knot, they tying the ring on with a second square knot and putting a half hitch in each end of the line to keep the second square knot from coming undone.
It works, but I figure there's a "right' way to do this that doesn't look so ugly.