Abstract: In the production of a matched set of golf clubs, the most accurate method for matching the flex of each shaft in the set is through the use of an electronic frequency analyzer which measures the vibrational frequencies of the shafts or clubs. With most high quality steel shafts, such frequency measurements are generally reproducible and serve as a reliable index of shaft flexibility. It has been found for some shafts, particularly for composite shafts, that frequency measurements taken along different cross-sectional diameters may vary. For such shafts, it has been found that frequency measurements will be reproducible, if the frequency measurement is made on the same diameter. The diameters used for such measurements are marked on the shaft and then employed in the construction of the golf club, such that the diameter is substantially perpendicular to the striking face of the club head.