At first look I couldn’t imagine why someone would use this since the slots on the front and prongs on the back are the same size. It then occurred to me that it was probably used with the single receptacle plates that have a spring loaded cover. It would keep the cover from pressing down on the wires of whatever was plugged in. You can see one of those covers by going to
EE1004Has some minor wear to the knurling. Marked 100W and 110V
