Does it really matter? (Honest question, not trying to be an ass). I was a fueler many years ago, and all of our training (official videos from aeroshell or whoever) stated to attach the ground line to any metal part of the airplane that was in contact with the frame. They specifically mentioned both exhaust ports and landing gear. Why is the exhaust port not acceptable (Now obviously, if a guy had obviously chromed or polished exhaust ports, I wouldn't clip the ground line on there because of courtesy, but that's just me).