DIN 17100, a German standard for structural steel, defines strict dimensional tolerances to ensure interchangeability. For thickness: ±0.3mm for 3-6mm, ±0.5mm for 6-10mm, and ±1% for thicker sections. Width tolerances range from ±1mm (for 20-50mm width) to ±3mm (for 200-300mm width). Length tolerances are +50mm/-0mm for bars up to 6 meters. These tolerances control variations from rolling processes, ensuring flat steel fits precisely in assemblies. For example, a 10mm thick × 100mm wide bar must measure 9.5-10.5mm in thickness and 98-102mm in width. Compliance is verified via calipers and laser measurement during quality checks, preventing issues in welding, bolting, or fitting with other components.