US Patent 7228981 Blow-molded hourglass container with helical rib and method of manufacture

A plastic container includes a body of one-piece integrally blow-molded construction. The body has an hourglass shape in side elevation with a waist, a base and a shoulder, and at least one helical external rib extending at least one full turn around the waist. The hourglass shape provides as a result of the blow molding operation minimum hoop stretch and extra thickness and strength at the waist, and maximum hoop stretch and minimum thickness at the shoulder and base. The helical rib at the waist of the container gives mechanical stiffness and resiliency for gripping and squeezing the container at the waist, yet allows angular movement of the shoulder with respect to the base to enhance flexibility.