... tri-cone rock bits with metal-sealing bearing system for oil well drilling.Main structure features:1. This ... -cone rock bits for well drilling: 1, Very soft with low compressive strength, such as soft marl, clay, ... 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 ...