... tri-cone rock bits with metal-sealing bearing system for oil well drilling.Main structure features:1 ... 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, ...