... for oil well drilling: Type IADC Bit Sze (inch) Standard API pin shank size (inch) Wight (KG) ... marl, clay, unconsolidated sandstorm, salt, etc. Recommended Bit type: GHJ437, Drilling weight: 0.35~0.90 ... shale, clay, sadstne, soft limestone, etc. Recommended Bit type: GHJ517, Drilling weight:0.35~1.05 ... hard shale, soft limestone, sandstone, etc. Recommended Bit type: GHJ537, Drilling weight 0.5~1.05 ...