How can the material of rod have a spine? what is the spine of rod

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.
Theoretically speaking, all materials have a spine, but the degree is different. Everyone often sees the promotion of "uniform wall thickness" in order to avoid the spine. The density difference of the fiber arrangement will also cause the spine.
If the spine is used as the most stressed side, it will largely avoid breakage caused by excessive tension

How should we find the spine of the fishing rod?
1. Bend the fishing rod slightly and slowly turn the fishing rod. When it reaches the spine of the rod, no more tension is felt.
2. Observe the radial rolling thickness of the fishing rod, the relatively thicker side is the spine of the fishing rod

After finding the spine of the fishing rod, we need to check whether the span is on the side of the fishing rod with the greatest force
For a straight rod, the "spine" should be on the top (the back of the guide ring), while the gun handle is just the opposite.

If the fishing rod does not find the right "spine" or does not find the "spine" during the process of winding the guide ring and assembling, the rod body will twist when it is stressed, which may have a negative impact on the use.