Our drill collars are manufactured from 4145h modified steel. \n\ndrill collars are bored and drifted to api spec7-1 and fully heated to meet or exceed the mechanical property requirements of api spec7. hardness range of 285-341hb and a charpy v notch impact value of 54joules are guaranteed one inch below the surface. \n\nsress-relief features are manufactured in compliance with api spec7, unless otherwise specified by customers. shenlong offers optional elevator and slip recesses to improve handling efficiency and safety.