One of the most time consuming tasks with detailing in Revit is cleaning up dimensions. By default when dimensioning an element, the dimension extension line extends to the element with a slight preset offset. The time consumption of dragging each extension line to a point where it doesn't intersect another dimension line is phenomenal. This post will describe how to do this automatically.
1. Select a dimension string and click edit type.
2. Click Duplicate and name the new dimension type. You can rename this later if desired.
3. Now scroll down to "Witness Line Control" under the Graphics category and change the value to "Fixed to Dimension Line".
4. Next go to the "Witness Line Length" parameter and change its value to 1/2". Now click OK.
You will see that ALL of the extension lines are now a preset length.