1.best heat treated 2.first class alloy steel 3.durable impact parts 4.high speed,most stable perfomance 5.easy to maintain Usage: Drill holes from 305 mm to 350mm.Matched products: drill rods with API 5 1/2"REG BOX bits with Ql100,MACH100,SD10 shanksApplication fields: all kinds of fields, such as mining, quarry, tunnel, bridge, construction and etc., but extremely exellent to use with casing ...