30 Oct PUREing vs. Spine Alignment vs. FLO
Spine alignment, FLO and SST PUREing all try to install a shaft in its best orientation, but they measure different things. Spine alignment finds the stiffest side. FLO finds the plane where the shaft vibrates in a straight line. SST PURE measures the shaft all the way around and finds the plane where it bends most repeatably, accounting for straightness, roundness and stiffness together.
Why orientation matters at all
A golf shaft isn’t perfectly uniform. Small manufacturing variations in wall thickness, straightness and stiffness mean it bends a little differently depending on which way it faces. Each method below is a way to choose that direction on purpose instead of by where the logo happens to sit.
Spine alignment
A shaft’s “spine” is the direction in which it’s stiffest. Builders find it by flexing the shaft in a spine-finding tool and rotating it until it settles in one position, then install the shaft with the spine in a chosen orientation.
The limit: spine alignment looks at one property, stiffness, with the shaft bent in a static position. A swing is dynamic, and stiffness is only one of the variations that affect how a shaft moves.
FLO (flat line oscillation)
To FLO a shaft, the builder clamps the butt end, flexes the tip so it vibrates, and watches the motion. Many shafts vibrate in an oval or wobble. The builder rotates the shaft until it vibrates in a flat line, marks that plane, and installs the shaft with it facing the target.
The limit: FLO is usually done by eye, so results depend on the builder and the setup, and it produces no measurement to check or repeat.
SST PURE
An SST PURE machine tests how the shaft behaves as it bends in orientations all the way around its circumference. Software analyzes those measurements together and identifies the plane of most repeatable bending, the Plane of Uniform REpeatability. The machine marks that plane, and the shaft is installed with it aligned to the target.
Because it’s measured by machine, the result is consistent from shaft to shaft and builder to builder, and it can be quantified. In a Plugged In Golf test of 36 shafts, PUREing reduced off-plane movement by an average of 75.2% in graphite shafts and 64.7% in steel.
Side by side
| Spine alignment | FLO | SST PURE | |
|---|---|---|---|
| What it finds | The stiffest direction | The plane of flat vibration | The plane of most repeatable bending |
| What it considers | Stiffness | Vibration pattern | Straightness, roundness and stiffness together |
| How it’s measured | Static flex, by hand | Plucked vibration, by eye | Machine measurement and software analysis |
| Repeatable between builders | Varies | Varies | Yes |
| Produces a measurement | No | No | Yes |
Frequently asked questions
Is PUREing the same as spine alignment?
No. Spine alignment finds the stiffest side of a shaft. PUREing finds the plane where the shaft bends most repeatably, considering more than stiffness.
Is PUREing the same as FLO?
No. FLO is a visual test of how a plucked shaft vibrates. PUREing is a machine measurement of how the shaft bends all the way around.
Can I spine or FLO a shaft and then PURE it?
There’s no need. PUREing determines the installed orientation, so it replaces the other methods.
Read next: What Is SST PURE? · Which Shafts Benefit Most?