Line thickness indicates the thickness of the writing produced by a particular writing instrument on paper or other surfaces.

The ball diameter indicates the size of the ball found in a writing instrument, such as a ballpoint pen, which is responsible for transferring the ink. In some brands, this value is specified instead of the line thickness of the pen. There may be a difference between the ball diameter and the line thickness, as they do not necessarily correspond to each other.

Special features are added values that facilitate the everyday use of the device in everyday life or give the writing instrument a unique characteristic.