... section pipes and rectangular hollow section pipesSpecifications30*30-600*600 mm,30*20-600*550mmThickness3-25 mmMaterialQ235B ,Q345B,20# , ... 's requirement 500*500 mm square steel tube, seamless square steel tube ,seamless rectangular pipe ,400*400 mm square steel tube ,350 ... *350 mm square steel tube ,450*450 mm square steel tube ,500* ...