... Milled tooth bits1,Soft formations(114-117)These bits are designed to drill the softest formations such as soft shales, ... formations(121,124,126,134,136,137)These bits are designed to drill formations such as shales, medium soft limestone, ... to hard formations(213,214,215,217)These bits are designed to drill formations such as hard sandstone, dolomite, and ... , 617G, 627G, 637G API 8 1/2" steel cone bit