Differences Between Drill Rod, Round Bar and Steel ...
Drill Rod Hardness and Machinability. The rods are manufactured of annealed tool steel (O-1, A-2, D-2, H-13, S-7, M-2, or W-1). Then they are cold drawn and (usually) polished. The drill rod hardness is affected by the cold drawing manufacturing process. The hardness is greater for the small diameters as show by the table below.
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