**System Information**
Acer ES 17,Windows 10
**Blender Version**
Broken:2.79b;Hash f4dc9f9d68b
Boolean Modifier doesn't divide form from object{F4806418}
1.Click the cone-like "cable-holder" with the three rings around.
2.Add Boolean modifier
3.Boolean modifier=Operation=Difference
4.Boolean modifier=Object=Circle.002(selects the three rings attached to the cone)
5.Apply!
6.Nothing happens when the three rings get pulled off!
I created the three rings with a simple circle.
Added a face via "f" in Edit mode.
Extruded it, made it smaller.Deleted the big faces and solidified it.
The half-rings are created with the knife tool.