The Porter-Cable 43550PC is a Classical Stile 3/8 inches Tongue Router Bit. It is constructed of 4140 alloy steel, a harder grade of steel than standard cast steel bit bodies. The is annealed and heat treated to Rockwell hardness of 40-45% harder than is possible with cast steel bodies. The bits are precisely ground using computer controlled machining for precision tolerances and perfectly concentric shafts. The carbide tip is made from a specially blended micro grain carbide for superior results and longer lasting sharpness.