We can manufacture square drill rods and hexagonal drill rods as per requirements of customers. They are made of AISI 4142H-4145H forged or rolled alloy structural steel.  Quenching plus tempering thermal treatment will be conducted over the whole length. Its Brinell hardness can reach 285-341 on the basis of such thermal treatment. Charpy impact energy: 54J. The formulated process can ensure that the misalignment of the hole reaches the standard wall thickness. Kelly bars are manufactured according to the technical code API.