How are round steel specifications typically expressed?

Round steel specifications are primarily denoted by diameter (Φ) in millimeters, often supplemented by length and weight per meter. For example, "Φ20" means round steel with a 20mm diameter; "Φ50×6000" indicates 50mm diameter and 6000mm (6m) length. Common diameter ranges from Φ6 (light-duty, ~0.22kg/m) to Φ300 (heavy-duty, ~441.8kg/m). Weight per meter is calculated via the formula: Weight (kg/m) = 0.00617 × Φ² (derived from steel density 7.85g/cm³). Lengths are usually 6m, 9m, or 12m (fixed-length delivery), while "random length" (3-12m) is available for small-batch orders. Some high-precision round steel (e.g., for shafts) also specifies tolerance grades (e.g., h9 for diameter tolerance ±0.036mm for Φ20).