Construction geometry tools enable you to place temporary lines and circles in your model. Construction geometry are not drawing objects; they are used as references.
Snaps can be used on construction geometry for creating model geometry, as well as other construction geometry. However, because construction lines are infinite, the Vertex and Middle Point snaps are not available.
You can display the Construction toolbar by right-clicking in any toolbar area and selecting Construction. 
These tools are also available on the fly-out toolbar from the Drawing Tools.
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Note: You can use construction entities with the Trim tool to trim other drawing entities, however you cannot trim construction entities themselves.
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