THIS IS A 5/16" ROTARY CUTTER. This a 5/16" Double end spot weld cutter, Double ended cutters extend tool life. Arbors fit any 1/4", 3/8" or 1/2" chuck hand held drill. Cut around the weld to help remove damaged panels fast without harming the underlying panels. Hollow design cuts around the weld, thus hardness does not affect tool sharpness.