... bits for well drilling: 1, Very soft with low compressive strength, such as soft marl, clay, unconsolidated sandstorm, salt, ... Rotary speed, 300~60 r/m.2, Soft with low comprssive strength, such as shale, clay, ... sadstne, soft limestone, etc. Recommended Bit type: GHJ517, Drilling ... speed, 200~40 r/m. GY series insert tri-cone drill bits for oil well drilling