... /2" ~ 6-5/8" REG. GHJ series tri-cone rock bits with metal-sealing bearing system for oil well drilling ... -5/8REG 60 Drilling parameters of GHJ series tri-cone rock bits for well drilling: 1, Very soft with low ... , 220~60 r/m.3, Medium soft with hard abrasive treak, such as hard shale, soft limestone, sandstone, etc. Recommended Bit ... speed, 200~40 r/m. F/FC series tricone rock bits for oil well drilling