Understanding Dimension Annotation Elements

Dimensions can be categorized into two types and have various components.

• Dimension Types Driving

• Driven

• Dimension components Dimension text

• Dimension line

• Extension line/ witness line

• Offset line

• Leader

• Geometric tolerance frame

• Datum feature symbol plunger

Figure 1 - Dimension Text, Dimension Lines, and Extension Lines

Figure 2 - Leaders and Frame

Figure 3 - Datum Feature Symbol Plunger

Understanding Dimension Annotation Elements

Figure 1 - Dimension Text, Dimension Lines, and Extension Lines

Figure 2 - Leaders and Frame

Figure 3 - Datum Feature Symbol Plunger Dimensions can be categorized into two types and have various components:

• Dimension types include Driving and Driven dimensions: Driving dimensions control or drive model geometry if their values are updated. These are dimensions that are naturally created during the solid modeling process, and can be shown on the model during the annotation process.

• Driven dimension values are controlled or driven by model geometry. Their values update as geometry changes. These dimensions are created by referencing existing geometry during the annotation process.

• Dimensions utilize common components that are often referred to during annotation creation: Dimension text — The numeric dimension value, text, and symbols.

• Dimension line — Lines extending from the dimension text that display the extent of the measurement, and typically end with a symbol such as an arrowhead. In the case of angled dimensions, dimension lines become arcs.

• Extension line — Extension lines (also referred to as witness lines) project from the dimension line arrows to the model geometry.

• Offset line — Offset lines occur when a referenced piece of geometry is offset from the end of the extension line. This may occur if the dimension is created and then moved to a plane offset from the surface of the feature that was dimensioned.

• Leaders — Leaders serve as a combination of dimension and extension lines for some dimension types, leading the eye directly from the dimension text to model geometry. Leaders typically end with a single or double arrow, but other symbols can be used. Leaders also typically include an elbow, which is a short line segment extending from the dimension text.

• Geometric tolerance frame — A series of connected rectangular boxes containing geometric tolerance information.

• Datum feature symbol plunger — Often illustrated as a triangular symbol that attaches to a surface, datum plane, or geometric tolerance to define a control datum.