A 5mm (the size most current and recent rear der's use for the hanger mounting bolt) placed in the der's mounting bolt while the der is mounted provides enough leverage for minor hanger corrections when the hanger is AL. A long and thick flat blade screwdriver placed behind the hanger, wedged between the small cog and drop out, adds leverage for more force. Since most hanger bends are mostly all inward this is a fast and easy method to fix most bends. Andy.