What type of roller set is used primarily for creating volume in fine hair?

The correct choice is the on-base set, which is specifically designed to create maximum volume in fine hair. In this technique, rollers are placed directly on the base of the hair section, which allows for the greatest amount of lift and volume at the roots. This method is particularly beneficial for clients with fine or limp hair, as it enhances the overall fullness and body of the hairstyle.

Using this approach, the base of the roller supports the hair more directly, resulting in a fuller appearance when the hair is styled. Additionally, on-base sets contribute to a more defined curl or wave, further increasing the volume.

In contrast, the other roller techniques do not achieve the same level of volume. The rectangular set is typically used to create a more controlled and uniform wave rather than explosive volume. The off-base set positions the roller away from the scalp, which provides softer curls but less lift. The half-off-base set strikes a balance between lift and softer curls, but it does not achieve the same dramatic volume as the on-base set. Therefore, for creating volume in fine hair, the on-base set is the most effective technique.