Drill collar is mainly used to provide bit weight to drill bit so that drill pipe is in tension. Especially drill collar can keep drill bit centralized and hole track by large rigidity. Drill collar are manufactured strictly from API Spec.7 and SY5144 standard. Drill Collar are manufactured from AISI 4145H modified steel, and are supplied in the "as rolled" surface finish condition. Alternative surface finishes can be provided. Full-length heat treatment processes ensure that mechanical properties meet or exceed API Spec 7 requirements. A hardness range of 285-341, Brinell Hrdness and Charpy "V" notch minimum impact strength of 54J(40ft-lb)at 21℃±3℃(70±5)are guaranteed one inch below the surface. We inspect all our drill collars to comply with API standards.