Traditional Banjo Inlay Set.
John Greven who has extensive knowledge in this field gave this information to me;
Mastertone banjo RB-12.  This Gibson was the only one of their banjos that had a highly radiused fingerboard, all the rest were flat as were most banjos of the time.   It is also the only "Mastertone" series banjo that did not have the typical "MASTERTONE" engraved block inlay on the 21st fret.  It was made in the early 40's and they no longer had Frank Pirazzo doing their inlays  and had to keep it simple to be able to do "in house".
John