Frequency Matching and “Flo” are really different things and both can be important if the goal is to eliminate any inconsistency that can when assembling a set of clubs. First, with regards to “Flo” or “Spine” or what our preferred method of Pureing. These processes or procedures are designed to identify a neutral plane or principle plane of oscillation in golf shafts. It is necessary because no shaft is perfectly straight or perfectly round and because of this can flex differently depending on the way they are oriented in a head. The Pureing process, which is the most precise by far, identifies the neutral plane and when installed, the shaft will perform consistently, like it would if it was perfectly straight or perfectly round. So if you want to eliminate inconsistencies in the way shafts will load and unload, some form of orientation identification should be done and Pureing is the most precise.
Frequency matching can occur naturally in sets where shafts are consistent (should still be Pured) in flex, head weights progress like they are suppose to (7 gram increments through the PW) and lengths progress in 1/2″ increments. Frequency is defined as a time measurement of a golf shafts oscillations to determine relative stiffness and is usually expressed in CPM’s (cycles per minute). I started in this business analyzing players sets using one of the first Frequency machines. When the oscillations from one club to the other was inconsistent, it indicated that either a few shafts in the set needed to be changed or all the set needed to be reshafted with “frequency matched” shafts. Frequency gave us a way, and still does, to identify inconsistencies in shafts under a load and in motion. The drawback to frequency matching is that it really does not tell us the flex distribution the entire length of a shaft. Still, it is a way to fine tune the flex feel and consistency within a set.
There is a whole lot more that could be said probably needs to be explained on these subjects, but above are the very basics. As we teach in our Advanced Shaft School, if you want to eliminate every inconsistency that can occur due to the tolerances that are inherent in the manufacture of golf shafts in todays market, you should have shafts Pured (or some form of orientation identification) and frequency matched.