Steel round bar refers to a circular cross-section of solid steel bar. Its specifications to a few millimeters in diameter that if "50" means that a diameter of 50 mm round bar. 
Divided into hot-rolled bar, cold forging and drawing three. Specification for hot-rolled bar of 5.5-250 mm. Which :5.5-25 mm, most of the small bar to bar into a bundle of supplies, used in steel, bolts and various machine parts; more than 25 mm, round steel, mainly used in the manufacture of seamless steel tubes for mechanical parts or blanks.