The Shaft Glossary, Plain and Simple
Four terms that matter more than the flex letter printed on the shaft — and none of them can be judged from a label alone.
Spine Alignment (FLO)
Every shaft has a slightly stiffer side from the manufacturing process. Flat-line oscillation testing finds that stiffer plane and orients it consistently in the clubhead, which can quietly affect face angle and start line if it's ignored.
Kick Point
The point along the shaft where the most bending occurs during the downswing. A lower kick point tends to help launch the ball higher; a higher kick point generally produces a flatter, more penetrating flight.
Torque
How much a shaft twists around its own axis under load. Lower torque usually feels more stable for faster, aggressive swings, while higher torque can add feel and a softer release for smoother tempos.
The Flex Label Problem
"Regular," "Stiff," and "Extra Stiff" aren't standardized across manufacturers — a "Stiff" from one brand can play noticeably differently from a "Stiff" from another. Frequency, not the label, is what we actually measure on the board.
Frequency Matching, Explained
Every shaft has a measurable frequency, expressed in cycles per minute (CPM), when clamped and set oscillating on the board. In a well-built iron set, frequency should step up by a small, consistent amount from the longest club to the shortest — usually 4–5 CPM per club.
When that progression is uneven, clubs in the set can feel like they're fighting each other even though every one of them is individually well-made. Matching frequency across the set is one of the fastest ways to make a full set of irons feel like one continuous tool instead of fourteen separate decisions.
Want the Deeper Explanations?
Field Notes covers each of these topics in more depth, or bring your own questions straight to a bench session.