Abstract: Flanged steel wheels remain in service on rail cars, locomotives, and other heavy rail guided machinery unitl they no longer maintain minimum specified rim or flange profile dimensions. If the rim or flange profile of the wheel cannot be returned to minimum specifications by surface machining operations, the wheel is condemned as being defective and is removed from service and scrapped. It is desirable to use an automated inspection device to determine if a wheel is approaching this condemning limit of profile wear. The invention automatically detects profile defects upon passing the wheel between rail mounted antennae which form a resonator cavity and transmit microwave radiation. When influenced by a wheel possessing condemnable rim thickness, flange thickness, or flange height profiles, the antennae cause a D.C. voltage to propagate at a microwave detector inserted into an interconnected comparison bridge network.