Create and use object guides
Although ruler guides are useful for aligning objects and providing visual reference, it is sometimes useful to have a more complex shaped guide. Another option is to use any regular path—even curves, ellipses, and so on—as a guide (called an object guide or a guide path).
To create an object guide from a selected path
Select a path to use as an object guide.
On the Object menu, point to Guide, and then click Make, or press CTRL+5.
You can also right-click the object and click Make Guide from the menu that appears.
When you convert a path to an object guide, the fill and stroke attributes disappear and the guide appears as a thin, semitransparent line on top of all other graphics objects.
If the Snap to Guides feature is enabled, objects will snap to these object guides in the same way they snap to the page grid or ruler guides.
To enable or disable Snap to Guides
On the View menu, click Snap to Guides.
You can also release the object guides in your document so that they become ordinary graphic objects again.
To release all object guides
On the Object menu, point to Guide, and then click Release (or press CTRL+SHIFT+5).