An electrical outlet box molded of plastic material has a knockout arrangement in a box wall that is formed by inner, intermediate and outer circular grooves that are eccentrically positioned to overlap at a tangent location and define inner, intermediate and outer eccentrically positioned circular knockouts. The grooves vary in depth from a minimum depth at the tangent location to a maximum depth opposite from the tangent location. Areas of increased weakness are provided in the box wall at the bottoms of at least the inner and intermediate grooves, and screwdriver slots are provided in the knockouts opposite from the tangent location.