Tekla "Object Hanging" Structures

Hello everyone, 

Please, I am a beginner on Tekla structures, I use it for the drawing in metal frame, and I have a problem on the drawing, 

Here is the ^porbleme:

when I launched the list of drawings, set, assembly, I entered one of the drawing boards to see what is missing as a dimension, so I wanted to add dimensions by the mouse, but the problem is that I couldn't snap the limits of my objects despite that all the controls of the snapping are active, The hanging controls at the bottom are all active but he doesn't give me the hand to hang them, please, can you help me solve this problem, 

Thank you very much for your help.

Good evening

Look there to see if you find what you are looking for.

https://teklastructures.support.tekla.com/fr/190/fr/ext_dimensioning_tool