DIN2391 EN10305 BK .NBK, GBK Precision Cold Drawn Seamless Steel tube Brand : Zhongxing Steel Pipe (by ourselves) Specification : OD18mm to 121mm , Thickness 2mm to 18mm 0ur products are offered in standard as well as customized specifications given as per client.1.Section shape : Round2. Material Specification and Ref. Document ST52,BK+S OR NBK,DIN2391 OD:36-480mm WT:3-40mm