... series tri-conerock bits for oil well drilling: Type IADC Bit Sze (inch) Standard API pin shank size (inch) ... soft marl, clay, unconsolidated sandstorm, salt, etc. Recommended Bit type: 437, Drilling weight: 0.35~0.90 KN/mm ... as shale, clay, sadstne, soft limestone, etc. Recommended Bit type: 517, Drilling weight:0.35~1.05 KN/mm ... speed, 200~40 r/m. F/FC series tricone rock bits for oil well drilling