Gibson RB-1 #9527-6

This original five-string RB-1 is quite unusual in that it features the rare “Coke bottle” peghead shape, the diamonds and squares inlay pattern normally seen on style 3 banjos from the 1920s, and a Mastertone label inside the rim even though style 1 was a sub-Mastertone model.  At least one other banjo from this lot, #9527-18 (see Gibson banjo serial numbers vs. factory order numbers), is also known to have a Mastertone label although its inlay pattern is the conventional style 1 fleur-de-lis design.  Two other examples from lot 9527 are known with the diamonds and squares pattern as seen here.

Photos courtesy of Rich Craig.