With the time so many things have been added to club in the form of flexes, kick points, torques etc, one must have to consider the weight of the shaft as well for these all factors do have a considerable impact on the overall playing conditions.

Shafts' weight varies with the design and material used in it. For instance, a regular Apollo steel shaft with mid-kick point weighs about 5.19 ounces, the same shaft made from graphite weighs around 4.19 ounces. If we further go to boron graphite shaft, it weighs around 3.12 ounces, which still reduces if we exclude the boron. Without boron its weight becomes 2.6 ounces.

It has been noted that a lighter shaft allow player to generate higher clubhead speed. The clubhead have a higher percentage of the club's weight and eventually additional stress will be put on shaft as a result it requires more flex and torque. It concludes that a stiffer flex is required to have same playing conditions to a club with a regular weight shaft.

For heavier shaft, you can reverse the effect. That is, the clubhead has the lower percentage of the club's weight, which in turn reduces the amount of stress on the shaft. This shows that you need a more flex in this case.

Swing Weight

Swing weight basically determines the weight distribution within a club. It is to be noted that the higher the swing weights of a club, the heavier the clubhead in relation to shaft and grip. Similarly, by lowering the swing weight, you will get lighter clubhead in relation to shaft and grip.  

Swing weight normally influences the performance of a club and its shaft. Each component of a club, i.e. shaft, grip and clubhead maintains a dead weight, which determines its swing weight.

It is obvious that shifting from a regular shaft to a lightweight will reduce the dead weight of a club, but as the percentage of the dead weight is greater in the clubhead, the swing weight will also increase. As swing weight related to components in a club, changing any component will affect the swing weight.  

The major advantage of lighter swing weight is that it reduces the stress on the shaft during swing. If you ever fit identical shafts to a club with variable swing weights, the shaft will then on a club act like a stiffer shaft. To cancel out this phenomenon is the fact of receiving greater clubhead speed with the lighter club.

It is a tough task to find an optimum swing weight. It is, however, essential to go through some trouble to reach to the point where you find the best for you. The swing weight has different ranges in golf clubs, i.e. it normally ranges from C6 for juniors and women to D2 for men. Again important one should keep in mind is that modification in any of the component of a club will affect its swing weight accordingly.

You might also want to learn about Choosing a Golf Ball and Changing the Swing Weight of a Golf Club

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