It's my understanding that receptacles installed to metal boxes inside a wall (sheetrock) have to be of the self-grounding design in order to not be required to run a bonding jumper to the ground screw on the receptacle (bonded via 6-32s). Also, if metal box is surface mounted, a receptacle not of the self-grounding type and using an industrial raised cover is considered bonded [after removing the insulated washer(s) ] and not required to have a jumper as I just described, BUT if the industrial cover is not raised then it is NOT considered bonded.
Now, if I install a switch to a metal box inside sheetrock as long as I use metal screws the switch is considered adequately bonded. 404.9 (B) (1). Is it just the simple fact this is not a receptacle?
314.25(A) Nonmetallic or Metal Covers and Plates - Where metal covers used, 250.110 applies - "Exposed, normally non-current carrying metal parts of fixed equipment supplied by or enclosing conductors or components that are likely to become energized shall be connected to an equipment grounding conductor....."
I've never seen a 1900 blank with a bonding jumper on it...... So again only the 8-32s are the required bonding method.
Maybe I'm splitting hairs here but is this a contradiction where a receptacle is not considered bonded by just using the 6-32 screws (no self-grounding design) but switches, blank plates, etc... are??