I was recently speaking with a guy who owns his own electrical contracting business. He is currently taking inspector classes for NJ and the topic of self grounding receptacles came up. He told me that in the class they were teaching them that in a "1900 slap-on w/ mudring" situation self-grounding receptacles shall not be used as per NEC. Section 250.142 (B) mentions that self-grounding receptacles shall be permitted with flush-type electrical boxes. So, is a mudring and 1900 slap-on not considered a flush type box, or are they teaching this subject incorrectly in the class? It was always my understanding that the screw threads completed the grounding path in this and similar situations, thus making a self-grounding receptacle a relevant product.