Here is a list of the parts of a dimension along with their descriptions.
Dimensions have several distinct elements: dimension text, dimension lines, arrowheads, and extension lines.
Dimension text is a text string that usually indicates the measurement value. The text can also include prefixes, suffixes, and tolerances.
A dimension line indicates the direction and extent of a dimension. For angular dimensions, the dimension line is an arc.
Arrowheads, also called symbols of termination, are displayed at each end of the dimension line. You can specify different sizes and shapes for arrowheads or tick marks.
Extension lines, also called projection lines or witness lines, extend from the feature to the dimension line.
A center mark is a small cross that marks the center of a circle or arc.
Centerlines are broken lines that mark the center of a circle or arc.