A mandrel is provided with a plurality of oval sections of varying circumference formed thereabout. The circumference of a first oval section is between about 1.75″ and about 2.6″. The circumference of a second oval section is about 0.2″ to 0.9″ greater than the circumference of the first section. The circumference of a third oval section is about 0.2″ to 0.9″ greater than the circumference of the second section.