Original 5 String 1926 Gibson Mastertone RB-3, Ball-bearing, FON 8447-7
In 1926, Gibson experimented with a ball bearing system of supporting the tone ring. Part of the reason for this was that the skin heads of the day were subject to humidity and heat, but it was also seen as a design improvement. The ball bearings are supported by a system of strong springs, the intent being to hold the head at a constant tension. The tone ring is a cylindrical shape with holes, unlike the later years flat head and arch top rings, although the outside profiles is the same as an arch top, and it appears to be an arch top until one learns it's a ball bearing.
