Although thread rolls are perishable tools, they generally do not wear. Thread roll failure is due to stress and/or fatigue. In some cases such as going over center, having an oversized blank, short feed out, etc., the rolls may gall on the pins. The gall will always occur on the adjustable roll (“A”) in the end away from the drive slot approximately 1/16 of an inch in. When gall is found, the roll and the pin must be returned for relap. The gall can not be polished out with normal equipment.