This is a Blair BLR13214 3/8" Double High Speed cutting bit. With twice the tool life is the unique 3/8" diameter hardened & precision ground cutting tool that makes removing spot welded body panels fast & easy. Hollow design cuts around weld, thus hardness does not affect tool sharpness. An adjustable depth rod sets the tool so only the outer panel is cut through, leaving the underlying panel undanaged. Cutters are packaged in sets of three. When one end becomes dull, simply unscrew the cutter from the arbor & reassemble with the new teeth exposed.