You know your flex. You might even know your weight. But there's a third variable that determines more about your ball flight than either of them — and almost nobody talks about it.
If you've ever looked at a shaft spec sheet, you've seen flex (Regular, Stiff, X-Stiff), weight in grams, and torque. Maybe kick point. Most golfers get to flex and stop there. Some get to weight. Very few get to kick point — and almost nobody gets to EI profile, which is the one that actually determines where your irons launch.
First: what is kick point, and why does it matter?
Kick point — also called flex point — is the position along the shaft where it bends the most during the swing. Every shaft has one. It's typically classified as low, mid, or high, measured from the tip end.
A low kick point is positioned closer to the clubhead. When the shaft loads and releases, it bends most in the tip section — which pushes the ball up. More launch, more spin. If you struggle to get the ball airborne with your irons, or you play on a course where stopping the ball on greens is critical, a low kick point is your friend.
A high kick point bends primarily in the butt section, closer to the grip. The tip stays relatively stiff. The ball launches lower and with less spin — a tighter, more penetrating trajectory. If your irons balloon in the wind, or you're hitting high enough already and want a more boring, workable flight, you want a higher kick point.
Kick point determines where within your optimal launch window your irons fly. The wrong kick point for your speed is robbing you of carry, trajectory control, or both.
Why 'Stiff' doesn't tell you this
Here's the problem with flex labels. They tell you how stiff a shaft is overall — roughly how much it bends under load. They do not tell you where it bends.
Two shafts can both be rated 'Stiff.' One might have a soft tip and a stiff butt. The other might be uniformly stiff from end to end. The first will launch higher with more spin. The second will fly lower and flatter. Same flex label. Completely different ball flights.
This is the fundamental limitation of buying a shaft based on its label alone. The label tells you one dimension of the shaft's behaviour. Your ball flight is determined by several dimensions simultaneously. Flex is necessary but not sufficient.
What EI profile goes even deeper
EI profile is a measure of how a shaft's stiffness changes along its entire length — a stiffness map from butt to tip. What matters is what it tells you: a shaft with a high EI at the butt and low EI at the tip has a loading pattern that's very different from one where EI decreases gradually along the whole length.
These differences in profile determine not just launch height and spin, but how consistently the shaft releases across the range of contact quality a golfer actually produces — not just on perfect strikes, but on the slightly thin ones, the toe-side ones, the ones on the 14th hole when your tempo has slipped.
This is the variable that most shaft recommendation tools ignore entirely. Brand charts certainly don't account for it. But it's the reason two golfers with identical swing speeds can be fitted into completely different shafts — because their ball flights, strike patterns and consistency needs are different.
What this means for your fitting
When you run your fitting through Play your Shaft, kick point and EI profile are both scored independently. The algorithm knows which shafts have a soft-active-tip construction (high launch, high spin, better for slower swings) versus a progressive-stiff construction (more consistent EI, better for faster, more consistent strikers).
If you report that your irons balloon in the wind, the algorithm scores low kick point, stiff tip shafts higher. If you report that you struggle to stop the ball on greens, active-tip constructions get a scoring advantage. This is why the fitting can produce meaningfully different recommendations for two golfers with the same swing speed.
Two golfers with identical swing speeds can need completely different shafts. Kick point and EI profile explain why.
The practical upshot
If you take one thing from this: don't buy a shaft based on flex alone. If you've ever been told you need a Stiff shaft and left with a shaft that still launches too high or too low, there's a good chance the kick point was wrong even if the flex was right. The fitting exists to catch exactly that.