Final answer:
The size and shape of the new curl formation in a perm are determined by the perm rod used during the perming process. The perm rod size directly influences the outcome of the curl's dimensions.
Step-by-step explanation:
The item that determines the size and shape of the new curl formation in a perm is the perm rod. When performing a perm, the hair is first softened with a perm solution which breaks the disulfide bonds of the hair. Then, the hair is wrapped around perm rods; the size of the rod dictates the size of the curl. Once the hair has been set on the rods, a neutralizing solution is applied to rebuild the disulfide bonds and lock in the new shape. This results in the hairstyle that may last for several months. While perm solution and neutralizing solution are both crucial in the chemical process of perming hair, hairstyle's shape, such as tightness and size of curls, are established by the perm rods used.