... high-grade alloy steel for assuring drilling efficiency. Because the drilling depth is usually up to dozens of meters, the strength and ... adopts low-temperature vacuum pervasion welding method to ensure the high efficiency and durable lifeSpecificationDrill Hole Diameterφ42,φ44,φ50,φ76,φ82Connection ... , 18×18,24×24Special service base on customer request. High-efficiency Comcined Drill Bit