Grit your teeth!
That is an open set that is merely a flatband that is a sort of
You might get away with casting diamonds in place but the common
method is to make the spread slightly larger than the stone, cut a
channel for the bearing seat, and hammer away till it's tight. A
gravermax makes the job easier but it takes a delicate touch. guess
you could call it a visible bearing set. Good luck and do any
engraving after you set the stone as hammering will distort.