Global Variable Part/Assembly

I have a Global Variable I created in a Part that is called Wall Thickness.  I create an assembly an add the Part with the global variable Wall Thickness.  I know I can reference the global variable from the part in the custom properties of the assembly with "Wall Thickness@Part.sldprt"  Here is my problem.  I will have an assembly with 2 different parts (Part Names will be different each time this assembly is used).  One part has a wall thickness of .25 the other .50  How can I pull these values into two different variables in my Assembly? 

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