Kelly is driving section of whole drill stem. Kelly are made from AISI 4145H-4145H Mod. alloy bars that are quenched and tempered full length, which up to 16meter long. A hardness range of 285 to 341 BHN and a minimum impact value of 54Joules as per ASTM A370 are maintained one inch below the surface at room temperature. All ends and center drive sections trepanned to provide true bores. They are drifted to API specifications, and all connections are phosphate-coated with an API thread compound.