I've seen 15A GFCI Receptacles with markings indicating a rating for 20A "feed thru"...
Do regular 15A duplex recepts have the same 20A feed thru rating? I haven't seen it listed as plainly as the GFCI's.
It's hinted at in the exception that allows 15-amp receptacles on 20-amp circuits. 15- and 20-amp receptacles of a given type ("pro", residential, spec, etc.) are internally identical.
The slot shape is the difference; they're rated by the plugs they are designed to reject. Note that 125- and 250-volt 20-amp receptacles both accept 15-amp plugs.
