The "spine" of a golf shaft is like a backbone. It can be visualized as a longitudinal line or plane on a golf shaft, that is more resistant to bending. All cylindrical objects have a spine including both steel and graphite golf shafts. The reason this matters is that if the spine of a golf shaft is not considered when mounting a clubhead, then that club will never play consistently. That's one club. Now imagine a bag full of clubs with spines randomly set. That's what you get with golf clubs off the rack, even a set of $800 Clubs or a $500 Driver.
Spine Alignment refers to finding the spine for each shaft and then aligning it perpendicular to the clubface (either at the 3:00 o'clock or 9:00 o'clock position). When the spine is aligned in this manner, the golf club becomes more stable, improving the golfer's ability to hit the sweet spot more consistently. Tests have shown that a golfer's ability to hit the sweet spot (impact repeatability) improved from 14% to 51% when they moved to spine aligned clubs. Missing the sweet spot by two-tenths of an inch will cost you six yards.
