Abstract: A moveable shaft insert assembly about 13 to 18 inches long weighing less than 50 grams is inserted into a hollow golf dub shaft wherein the depth of insertion of the shaft insert assembly may vary from about 1 to 10 inches. Changing the location of the shaft insert assembly allows a player to change the flex of the shaft and thereby optimize the performance of the club dynamics for that player for that day. The shaft insert is held in place by friction between the shaft and the shaft insert assembly. So shaft flex fitting can be administered by a player with or without coaching, and can be revisited at any time by a simple adjustment. The shaft inserts are useful on all hollow shaft clubs, and can be retrofitted to existing clubs without removing the grip.

Abstract: A moveable shaft insert assembly about 13 to 18 inches long weighing less than 50 grams is inserted into a hollow golf dub shaft wherein the depth of insertion of the shaft insert assembly may vary from about 1 to 10 inches. Changing the location of the shaft insert assembly allows a player to change the flex of the shaft and thereby optimize the performance of the club dynamics for that player for that day. The shaft insert is held in place by friction between the shaft and the shaft insert assembly. So shaft flex fitting can be administered by a player with or without coaching, and can be revisited at any time by a simple adjustment The shaft inserts are useful on all hollow shaft clubs, and can be retrofitted to existing clubs without removing the grip.

Abstract: The selectivity or the damping factor or the bandwith of a golf club can be determined by stimulating a club and measuring the rate of decay of the displacement, velocity, or acceleration. The resulting information provides a measure of the risk of off-speed swings from using a particular golf club and enables a better fit to be accomplished between a golf club and a player.