When you’re golfing with a driver, the flex of the club’s shaft affects both the feel of the club and the speed at which you can hit the ball. The flex you choose depends on the speed of your swing. For instance, if you can swing at about 60 miles per hour, you’d do well to choose a driver with a Ladies Flex shaft flex. Senior or A Flex drivers are good for swing speeds between 60 and 75 miles per hour while a Regular Flex shaft is tailor made for those with a speed between 75 and 84 miles per hour. Faster speeds need stiffer driver shafts. A Stiff Flex driver works well for golfers with a speed between 84 and 93 miles per hour, and an X-Stiff Flex is adequate for anyone that can swing their driver faster than 93 miles per hour, which is usually reserved for professional, championship-level golfers.