Oh, we are being technical. (Kidding)
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What you are describing is Flex. Spine is actually a characteristic imparted via the manufacturing process that runs the length of the shaft, where it is most resistant to flex. Think of it as a kind of back bone.
Isn' t what you are describing " flex" and what I am describing, the same as static spine???? If not, please explain. I am in no means an expert on this.