A vibration dampening insert for use in golf clubs includes a plug member located inside a shaft of a golf club. The plug member has a plurality of cavities formed therein, and a plurality of spherical weight members are disposed in the plurality of cavities. The plug member is made of an elastomeric...http://www.google.es/patents/US5718643?utm_source=gb-gplus-sharePatente US5718643 - Vibration dampening insert for golf clubs
