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Drill collars we produce is made from 4145H forging or rolling modified steel. Raw Materials are all from Top China Special Steel Group, so from the first beginning, we can assure high quality. We manage our Production and Inspection Process strictly according to API SPEC 7 requirements. All connections are phosphate-coated to improve resistance to corrosion. We can also do copper plating according to clients' requirements. We offer slip groove, elevator groove to improve handling efficiency and safety. Slip and elevator groove are machined in compliance with API RP 7G guidelines. We can also make stress relief groove according to clients' requirements. We provide free thread protector for both pin and box.