If I wasn't on the road working I could look at mine.
The threaded connection is for adding or removing the flip up deck extension which also has a light bar.
FYI if this is going on something newer you can't just plug into the truck trailer wiring. It will think you have a trailer and all...
They did survive the impacts. An extremely hot sustained fire took them out.
Do people really think they were prepped for demolition and then planes were precision guided into the floors where the collapse was to start?
Bldg 7 makes no sense though.