... /8REG 98Drilling parameters of GHJ series tri-cone rock bits for well drilling: 1, Very soft ... 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 KN ... hard shale, soft limestone, sandstone, etc. Recommended Bit type: GHJ537, Drilling weight 0.5~1.05 ...