... 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 ... 1, Very soft with low compressive strength, such as soft marl, clay, unconsolidated sandstorm, salt, etc. Recommended Bit ... speed, 250~60 r/m.3, Medium soft with hard abrasive treak, such as hard shale, ...