This machined plywood insert will fit most standard 2-1/8" cylindrical bores and allows the fitment of included classic forged brass rosettes with the minimum of overlap (2-1/4").
The insert is made from two glued together pieces of nominal 3/4" baltic birch ply and just thinner than a typical modern door allowing slight compression by the rosettes. Screw holes are pre-drilled for perfect concentricity. All you have to do is slide one side into the bore then screw the other side on.
Many case studies show these fit on the vast majority of cylindrical bore doors with no adjustments but it's recommended you buy one as a trial before installing many.
This is a vast aesthetic improvement over 3" retrofit rosettes and very easy to install. Sometimes they need slight sanding on the flat face two be thinner than the door. In some cases, crusts of paint need removed from the bore for a smooth fit. Every now and then, the recess in the edge of the door needs adjustment so the mechanical "backset latch" is concentric with the rosette.