How can the material of rod have a spine? The spine mentioned here refers to a certain area with greater rigidity in the longitudinal direction of the material. we also Just like a steel tube with a wall thickness of 2mm, a steel strip with a thickness of 1mm and a width of 2mm is pasted along the longitudinal direction, and the steel strip is tightly combined with the steel tube by welding and other methods. Then, when the steel tube is bent in the future, this direction is more difficult than other directions bending....