A strand that forms a pin curl is commonly defined in three major parts: base, stem, and circle.
The base is the area of the strand at the scalp, which is the foundation of the curl. This is also the area where the roller is placed.
The stem is the part at the beginning of the strand between the base and first turn, which demonstrates the direction and movement of the curl. This is also the area between the first turn of the roller and the scalp.
The circle is the remaining end of the strand which forms the curl (complete circle) and finally the wave. The width and strength of the wave will be determined by the size of the circle.
In a hair section, the stem determines how much movement, or mobility, the curl will have. The mobility is arranged by three categories: full stem, half stem, and no stem.
When a section of hair is molded in a circular movement to form a curl is called shaping. These can have an open- end or a closed-end. A pin curl should begin at the convex side, or open end, of a shaping.