I am designing a sheet metal trough to be driven by equations, which means extruding the profile of the trough a certain distance. I am unaware of how to set up the depth of the sheet metal piece to be linked to a global variable. As far as I am aware, I can not get the depth dimension to appear by any means of clicking on the feature itself in order to link it, like I would any other feature. This leaves me to manually typing in the depth dimension's name in the variable table, I assume. What is the nomenclature of the depth dimension of a sheet metal piece? Or is there an easier way to go about this?

I am on Solidworks 2019 SP4.0.

Thank you.