Bob, not to be a pain [Linked Image], I know you had the right idea, but an attachment plug is not a receptacle or cord connector as per UL.
An attachment plug is " a male contact device ...".
a cord connector is " a female contact device to be wired on flexible cord for use as and extension from an outlet to make a detachable electrical connection to an attachment plug or, as an appliance coupler, to a male inlet."

This specifically describes the 'cord connector' as being installed on a flexible cord, and not to a chapter 3 wiring method.

406.6 requires all cord connectors to be listed, that puts us in the direction of the manufacuturer's instructions and the UL White Book.

Pierre

Pierre Belarge