... REG. GHJ series tri-cone rock bits with metal-sealing bearing system for oil well drilling. ... series adopts non-isometry teeth placement in combination with optimized teeth height and shape.2. Applying ... rock bits for well drilling: 1, Very soft with low compressive strength, such as soft marl, clay ... 250~60 r/m.3, Medium soft with hard abrasive treak, such as hard shale, soft limestone, sandstone, etc. ...