... .35~0.90 KN/mm, Rotary speed, 240~60 r/m.2, Soft with low comprssive strength, such as shale, clay ... .35~1.05 KN/mm, Rotary speed, 220~60 r/m.3, Medium soft with hard abrasive treak, such as hard ... .35~1.05 KN/mm, Rotary speed, 200~40 r/m. F/FC series tricone rock bits for oil well drilling