Snap to vertex or edge does not work I want to join two sides of an object.
1. I used Knife Project to mark both sides of the object with a circle.

2.Then I deleted the marked faces.


I selected the edges of the hole created from the one side
I turned on the magnet 
I extruded along the Y axis.  But I cannot get it to snap the the vertices on the opposite side of the object.
Although not 100% sure, I believe
1. I need to press and hold the Ctrl key while extruding.
2. I set the snap to option to Closest
3. I set the pivot point to active element


I did turn on "Automatically merge vertices moved to same location".  However, when I checked afterwards by clicking the remove doubles, 56 doubles were still removed.  So not sure how that is suppose to work.