Toolbox - Suppress Feature Based On Custom Property Value

I'm trying to work into using toolbox on our network. it's not perfect but it's a step in the direction we wish to go.

My question relates to using Equation manager to control the suppression of a feature.

I added a "Partial Thread Indication" feature of a revolve cut to show the show the thread length - which is suppressed when the thread length is the same as the bolt length.

I've added a custom Property to allow the choice of either "No Grade Specified" or "grade 5" or "Grade 8" and i would like to suppress/unsuppress a feature to give a visual indication of either grade 5 or grade 8 (i.e. the 3 or 6 lines on the head).

But i can't see how to get the "toolbox custom property" into the equation manager.

Any ideas?