Abstract: A hollow golf club shaft and a moveable solid shaft insert about 6 to 24 inches long wherein the depth of insertion of the shaft insert into the shaft may vary from about 1 to 10 inches. Changing the location of the shaft insert allows a player to change the flex of the shaft and thereby optimize the performance of the club dynamics to the player. The shaft insert is initially held in place by friction between the shaft and the shaft insert, optionally with a joining agent located therebetween, until a final setting of the shaft insert is determined. Then the shaft insert is permanently located within the shaft to make the club legal for play under U.S.G.A. Rules. Shaft fitting can be administered by a player with or without coaching and can be revisited at any time prior to permanent attachment by a simple adjustment. The shaft inserts are useful on all hollow shaft clubs, from putter to driver, and can be retrofitted to existing clubs without removing the grip.

Abstract: Golf clubs can be matched either to duplicate a favorite club or to produce a matched set of clubs by determining a spectral response curve of a club and then matching other clubs thereto at at least about its natural frequency.