Ring gauge is thickness. A 50-ring cigar is 50/64 of an inch across. A lancero might sit in the 38–40 range; a robusto often around 50; a thick toro can run 52–56 and up. The number is a measurement, not a quality score.
Diameter changes how a blend shows. More ring means more filler relative to wrapper, a different burn rate, and more room to place ligero inside the bunch. It does not magically add flavor. A thin cigar can be full; a thick one can be mild.
Length is a separate number. A vitola is the pair: length by ring, often with a traditional name (corona, churchill, perfecto).