... for well drilling: 1, Very soft with low compressive strength, such as soft marl, clay, unconsolidated sandstorm, salt, etc. Recommended Bit ... , such as shale, clay, sadstne, soft limestone, etc. Recommended Bit type: 517, Drilling weight:0.35~ ... 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