... REG. GHJ series tri-cone rock bits with metal-sealing bearing system for oil well drilling.Main structure features:1 ... wall; improving quality of well wall, protecting the back of leg and seal.4. Bit's bear is ... GHJ series tri-cone rock bits for well drilling: 1, Very soft with low compressive strength, such as ... Rotary speed, 250~60 r/m.3, Medium soft with hard abrasive treak, such as hard shale, soft ...