Steel tooth tricone bits are also named milled tooth tricone bit, “steel” means the teeth material is steel, actually it is a type of special steels 15MnNi4Mo and the surface of steel material is hard faced by Tungsten Carbide to increase wear resistance.
Milled means the teeth is machined by milling machine, so steel tooth tricone bits have another names “mill tooth tricone bits” or “milled tooth tricone bits”.
17 1/2 inches is always diameter of the first hole in deep well drilling, the formations are always soft in shallow section, so 17 1/2″ is widely used in worldwide.