NorKut grinding discs are made with rugged NorZon grain so it cuts fast and lasts long. Resin bonded to a unique backing which resists cracking and breaking, these discs can be cut down to any size up to the 1" core. Use the cores to grind �pinch� welds and other hard to reach areas. Two quick change mandrels allow NorKut to be used on most popular tools. 7/16"-20 thread is for use with hand held pneumatic grinders while the 1/4" mandrel is for use on automotive drills.