What distinguishes double stroke letters in calligraphy?

Double stroke letters in calligraphy are characterized by being formed using two or more pen strokes. This technique allows calligraphers to create letters that have a more pronounced and dimensional quality, enhancing readability and aesthetic appeal. The use of multiple strokes enables the artist to control the line weight and add nuances such as thicker downstrokes and thinner upstrokes, which are essential for creating contrast in letterforms.

In contrast, other options such as size, single pen stroke creation, or italicization do not define double stroke letters. The concept of size is unrelated to the number of strokes used, while a single pen stroke refers to a different style of lettering, and italicization pertains to the slant and form of letters rather than the method of execution. Therefore, recognizing double stroke letters is fundamentally tied to their construction through multiple strokes, allowing for greater expression and variation in calligraphic work.