... .high quality and reasonable price 1) taper angle(degree): 4.46, 6, 7 , 11, 122) shank size: hex ... hard and abrasive rock formations, a wide taper angle is normally used. Taper angles of 11 and ... rock formations, a narrow taper angle of seven degrees is used. A 7-degree angle can also be used if ... hole drilling, equipped with small power rock drills, like air leg rock drills, hand held rock drills, etc. ...