For these kind of rosettes the best method is as follows; Route a channel a little wider than the rosette inlays. Put Black and White purfling of a 2 Ring Rosettes set on the inside and outside of the channel.
Position these rosette segments in an even pattern around the center of the channel.
Spot glue the sections in place with super glue.
Last, Fill the spaces with epoxy glue dyed black.
Black Opaque resin dye seems to work best for solid black color.
These rosettes can be streached out or squeezed in to make any size from 4" I.D to 5.5" I.D.