Merge several mesh objects I want to merge two mesh that has the public points in both objects. The relationship between two objects like a circle and a circular ring that can perfectly contain the ring.

I have tried the Boolean operation, but it fails to do it. 

How to combine two objects and do not produce any break face?
Could someone give advice about how to do it?

Thanks in advance.

Some supplements,


I loaded the two .obj files in Blender, and they would be combined to a light bulb. The first mesh is a glass container and the second mesh is a metal thread.
They share the same edge on the top rim of the metal part(blue arrow). Both of them are not enclosed.

I had attempted to combine them using union operation(boolean operation). But, they couldn't join together, and I also tried to use join command, they could join together, but there was a round hole in the connection area(Blue arrow).
You can 


  Join


them and them and then merge the closest vertices with 


  Remove Doubles


But you two meshes have to have a common "merging line" (An edge with the same vertex amount and close distance to each other)