Historical
NEMA ANSI C78.20:2003
For electric lamps - a, g, ps, and similar shapes with e26 medium screw bases
Sets forth the physical and electrical characteristics of the group of incandescent lamps that have A, G, PS and similar bulb shapes with E26 medium screw bases, including the reduced-wattage versions.
NEMA: National Electrical Manufacturers Association [nema]