B-Grade Enamel Pins
A 'B-Grade enamel pin is a pin that is of less-than-perfect quality. There might be little scratches in the enamel, or dings in the metal, or the screen-printing might be slightly off. Think flaws that are not super noticeable unless you're looking close.
A 'C-Grade' pin is a pin with larger flaws that are much more noticeable.