Almost all rod blanks manufactured today are produced by wrapping graphite and/or fiberglass cloth around a steel mandrel. This process causes a slight unevenness in the hollow blank resulting in a soft and stiff side of the rod blank commonly referred to as the spine.
For best rod performance, you should find the spine of your rod blank and locate your guides and reel seat either on or opposite the spine. Aligning guides on the spine eliminates the possibility of rod twisting.
To locate the spine, place the tip of the blank on a solid hard surface (kitchen floor) with the butt end up. Place your index finger on the butt of the blank and apply enough pressure to slightly bend the blank. The blank will roll around to the soft side of the spine. This will be the natural bend of the blank every time.
On two piece rods, it can be difficult to find the spine of the butt section so focus on finding the spine on the tip section. If the butt section spine is located, mark it and align the two spines.