I have been trying to dimension a bolt that I downloaded form website McMaster. It won't let me put a dimension on the diameter of the bolt over the threads. When I select my two diameter lines and try to place the text I get the following message: "Could not creat reference dimension from the current set of selected items." I looked at the model and don't see anything out of the ordinary. I saved the model in SW2011 because it was created in an older version. Why can't I put a dimension on the diameter?