What Does Shaft Flex 6.5 Mean?

Shaft flex is an important factor in making a smooth swing that suits your swing speed. Any golfer that has been through the experience of purchasing golf clubs, especially woods, will be all too familiar with the LASRX (Ladies, Amateur, Regular, Stiff, eXtra-stiff) flex designations. This reasonably pronounceable abbreviation, LARSX, is now used in conjunction with the Brunswick Shaft Company patented numbering system.

On August 2, 1995, Brunswick filed a trademark application for THE SHAFT COMPANY with the United States Patent and Trademark Office which was approved under serial number 74713464. However, the trademark filing was marked as abandoned is on September 25, 1996. The trademark is owned by Brunswick Bowling & Billiards Corporation.  Brunswick subsequently sold its golf division off to Royal Precision in 1996

However, fewer golfers have been through the experience and encountered the numerical designations indicating shaft stiffness.

What does a Shaft Flex of 6.5 mean?

The equivalent of a 6.5 flex is the eXtra-stiff shaft under the LARSX labels.

The LARSX designation of shaft stiffness is followed by many of the manufacturers but few of the brands follow the same standard in assigning a label to the stiffness of the shaft. Buying a regular shaft from brand A will not necessarily mean that it provides the same features as a regular stiffness shaft from brand B.

All articles/discussions relating to shaft flex should be seen as indicative recommendations and you will benefit from a proper shaft fitting when deciding on the clubs that you purchase.

How is the Flex of a Shaft Measured?

In the LARSX system, manufacturers use a deflection board where the butt of the shaft is clamped while weight is hung on the tip of the shaft. The amount that the shaft bent, was used to rate the shafts stiffness. A major problem in this method is the lack of a standard in the deflection board hence differences in the flex from various brands.

A simpler and more consistent way to measure shaft stiffness was devised as described in Jeff Meyer, Area Under the EI curve.

Before going into detail let’s touch on some shaft terminology that we will encounter.


This measures the circular rotation of the shaft during the swing ranging between 2 and 6 degrees. Low torque is a result of less twisting of the shaft with a rougher feel while high torque is associated with a soft-feeling shaft that is less accurate than a low torque shaft.


A more accurate method to measure shaft strength and the number of vibrations a shaft produces although measurements can vary between machines. The higher the vibration count the stiffer the shaft.

EI Curve

Measurements were taken of the rigidity of the shaft along the length of the shaft, normally increases of 1 inch. This indicates the amount of bend at every point on the shaft that is considered a more reliable measurement than flex or frequency.


The top end of the shaft is located underneath the grip.

How to calculate the stiffness of the shaft?

Add up all the measurements taken in the production of the EI curve to determine the overall stiffness of the shaft

The area under the EI curve is the stiffness of the point where every measurement contributes equally to the stiffness of the shaft.

Divide the total stiffness of the shaft by the shaft length to determine the shaft flex.  The number is rounded to one decimal place in intervals of 0.5 and reported as 4.0, 4.5, 5.0, etc.

Now that we understand how flex is determined and measured, let’s see what it means when a shaft has a 6.5 flex rating.

Although there is no standard in the way that manufacturers label their shafts under the LARSX system, there is a semblance of correlation between the LARSX system and the Brunswick system.

Ladies flex (L) is similar to a 4.0 rating under the Brunswick system, while Regular (R) flex is comparable to a flex rating of 5. Provision id made for the less frequently used Regular Plus at a flex rating of 5.5, stiff (S) at 6.0, eXtra Stiff (X) at 6.5, and ultimately Extra Stiff Plus at 7.0

Final Thoughts

Measuring shaft flex varies between manufacturers depending on the deflection board being used. It would be useful if the industry can have some semblance of agreement on how flex is determined and classified.

Fortunately, the Brunswick method provides more consistent results and classifying shaft flex and hopefully provides more consistency in your golf swing.

Your thoughts on the industry measurement of flex and whether it should be standard will be highly appreciated in the comments section below.

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Nick is the founder of GolfSpan and an avid golfer. He's not quite a pro but has over 15 years of experience playing and coaching golfers worldwide. His mission is to bring the golfing community a better experience when it comes to choosing the right golf gear and finding the right setup for your game.

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