Shaft deflection is the bending of the shaft in the forward/backward direction to and away from the target at the time of ball contact. This is measured in millimeters as the amount that the center of the clubhead is off the shaft line. Lead is a forward position of the clubhead center towards the target relative to the shaft line, and Lag is a backwards position of the clubhead center relative to the shaft line. An increase in deflection represents more Lead at the time of contact. This will result in an increased angle of attack, a lower mark position on the club face, and a swing path that is more leftward. With increased deflection values comes decreased consistency. Thus, the best players in the world will show a low deflection value.
Shaft droop is the bending of the shaft downward as you look down the line. This is measured in millimeters as the amount that the center of the clubhead moves towards the ground (positive value) relative to the shaft line. It is important to note that the clubhead center of mass will always line up with the center of the shaft. Higher droop values are seen with a softer club and more raising of the handles. Shaft droop will affect the line of attack, lie angle, face angle and loft. Much like deflection, higher droop values are typically associated with reduced consistency, however, one should look for more droop than deflection. Droop can be decreased through stiffening your club, or less handle raising.
Shaft twist, measured in degrees, is the amount that the club twists towards the target (counter-clockwise from an aerial view is a positive twist). This helps the player square the clubface when closure rate is lower. Shaft twist is controlled by the amount of torque built into the club. Torque is a measure of a club’s resistance to twisting. Low torque is around 2 degrees, high torque is around 6-7 degrees. Players who tend to hook the ball will benefit from lower twisting club or lower torque. Players who slice, a club with higher torque may be more helpful. Players that have higher than average swing speeds will be wise to consider a club with lower torque. It is important to note that with any club feature, changes in torque will be most helpful to a player with a very consistent swing. The most important factor of a golf swing is the human factor, and it is key to remember that the perception and ‘feel’ of the club will ultimately have the biggest effect on your swing.
Shaft ratio is a fraction representation of deflection divided by droop. Thus, high deflective players will have a higher ratio. Ideally, you want this ratio to be as low as possible. A player can reduce their shaft ratio by choosing a stiffer club. When this shaft ratio is low and consistent, adjustments can then be made to the club to manipulate other factors such as face contact point, angle of attack, etc.