... alloy steel and premium tungsten carbide insert, plus state of art welding technology and multiple precision heat treatment to ... and are used in areas that contain a lot of rock and also in the oil field. longer life ... /8", 4.3/4",5.1/8", 5.5/8", 5.7/8", 6.1/4", 6.3/4", 6.5/8" 7.3/8" ... contact ustrade manager: cn1000271447name: abdllahchina yang API 4 1/4"kingdream 3 blades of drag bit for soft formations