Drill collars, both slick and spiral, are made from AISI 4145 H Chromium Molybdenum Alloy Steel and are fully heat treated to achieve a Brinell Hardness of 285 to 341 BHN. They have a minimum Charpy V-notch impact strength of 40 ft-lbs at 70°F and at least 13% elongation. These mechanical properties meet or exceed API 7-1 requirements and are effective one inch below the surface at ambient room temperature.