The "E" stands for Excluded. If you were to convert Revit Duct/Pipe to fabrication parts any item with a "E" would not be used during the conversion.
Thank you for your reply.
So do you mean it can be used in CADmep or CAMduct but not in Revit?
The Exclusion is defined in programs like Estmep, CAMduct or CADMep and is solely for the purpose of not using an item during designline. CADMep's equivalent to multi-route. The button can still be used by selecting that object individually. So yes, it is still available within Revit.
The exclusion will also work with Revit when doing conversion from native revit to fabrication parts