The drill collars are made of modified AISI 4145H chromium molybdenum alloy steel. These drill collar bars are full-length heat treated and water quenched to obtain ASTM A-370 mechanical properties. Full mechanical and chemical mill test certifications are supplied with all drill collars. These mill test certifications guarantee a hardness range of 285 to 341 BHN and an impact value of 40 ft.-lbs. at room temperature one inch below the surface.