Doubt with SPC in heat transfer (Steady State)

Hello again, 

 

I'm doing a tutorial, OS1080, and i didn't understand why is used SPC, with all the boxes of degrees of freedom uncheked. What the SPC is used for? The subcase is (Heat Thansfer (Steady State).  

I found something about SPC on Reference Guide. The first figure bellow.The Step 4, from tutorial, tell me to make this SPC. 

 

Thanks!

 

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