Abstract: A self-lubricating plug insert-type valve assembly is provided for use with inflatable articles of manufacture, such as footballs, basketballs, etc. The sealing plug through which the inflation needle is inserted is characterized by containing 3-12 parts by weight of a silicone grease for each 100 parts of rubber contained therein. Although contained as part of the rubber mix of the cured plug, the grease migrates within the plug and forms a continually renewed lubricant coating along the passage through which the needle is inserted and withdrawn.

Abstract: A set of golf club shafts for a set of golf clubs is made so that the natural frequencies of vibration of the shaft for the various clubs are matched. Each of the shafts includes a butt portion, a tip portion, and a plurality of stepped portions between the butt portion and the tip portion. The length of the butt portion, the length of the tip portion, and the length of all of the stepped portions except one is the same for all of the shafts. The length of said one stepped portion of each shaft is selected to provide the shaft with the desired natural frequency of vibration, and the difference in the overall length of two shafts corresponds to the difference in the lengths of said one stepped portion of the two shafts. The torsional resistance of each shaft is increased without increasing the weight of the shaft by providing a shaft with relatively large inside and outside diameters and a relatively small thickness.