I know there are several ways to make dimensions from different parts linked or equal.

But here is my problem. I need the two dimensions undefined, such that they can be draged or freely changed in the assembly since the dimensions are not defined or specified.  Hope I have make myself clear.

I have this question because I want to freely change the dimension in a part and, in the meantime I want the linked dimension in another part can change accordingly.

How do I make two undefined dimensions linked or equal in different parts?

Thank you very much! Any help would be so much appreciated.