The monstrances at my dad’s parish are two very different kinds:
One is a crucifix with a 4" window, and the luna a 4" ring with a foot and a vertical spring tab to hold the host against the ring. It slides into a slot behind the window.
The other monstrance is an 8" luna, comprised of 2 disks of glass, two interlocking brass rings, and the rest is just a stand which clips to the bottom of the rings, holding them securely closed.
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