Shaft Flex is a critical determining factor for both distance and direction. Generally speaking, more flex equals more distance but less control. Conversely, at a given swing speed, stiff shafts can result in less distance but more accuracy.

Shafts that are too stiff for a player will often feel "like a board". The unmistakable pop of a well struck shot is difficult to achieve. The directional tendency will be to the right for right-handed players with a corresponding loss of distance. Shafts that are too flexible will feel better but are more difficult to control.

The rule of thumb is to use the lightest, most flexible shaft you can handle. It is always better to choose a more flexible shaft than a stiff shaft if you are a borderline candidate.

If you know your swing speed or can have it tested, you can use the chart below to achieve an even more accurate choice of flex: