When purchasing deformed bars, the most critical factor is the Grade of Steel (e.g., Grade 40, 60, or 75 in the US system, or HRB400, HRB500 in the Chinese system), which determines the yield strength. You must also specify the nominal diameter (ranging typically from 6mm to 50mm) and the rib geometry, as the deformations are essential for ensuring a strong mechanical bond with concrete. Always verify the chemical composition, particularly the carbon equivalent, to ensure proper weldability if your project requires it.