Dustin, my Sauer is pushing a century old. I'll forgive it for the hair it's off in bolt fit.

A Greener requires a rib extension between the barrels, which obviously does not work on an OU. The similarity to a Kersten, which has extensions on the sides of the barrels, is that both have bolts which protrude from the frame when the gun is opened (on both sides, in the case of the Kersten) and engage extensions off the barrels when the gun is closed.