I found this wartime Thor NOS 4" x 9/16" wire wheel in its original box at a flea market yesterday. The box is beat up, but the attachment does not appear to have been used. It fits a Thor portable electric grinder or multmatic air tool using a 1/2" arbor. Note that the box says Independent Pneumatic Tool Company, Aurora, Illinois. I don't know exactly when the Independent Pneumatic Tool Company of Aurora, Illinois, making and selling Thor brand power tools became the Thor Power Tool Company of Chicago, Illinois, but it wasn't prior to WWII. Independent Pneumatic had several contracts and in 1941 they got $896,000 from the War Deparment and the Defense Plant Corporation to upgrade their facilities.