... marl, clay, unconsolidated sandstorm, salt, etc. Recommended Bit type: 437, Drilling weight: 0.35~0.90 KN/mm, ... shale, clay, sadstne, soft limestone, etc. Recommended Bit type: 517, Drilling weight:0.35~1.05 KN/mm, ... as hard shale, soft limestone, sandstone, etc. Recommended Bit type: 537, Drilling weight 0.35~1.05 KN/mm, ... Rotary speed, 200~40 r/m. F/FC series tricone rock bits for oil well drilling