Factory hole in roof with grommet ... what is it for ??

So .. I have this hole in my roof , filled with a grommet of sorts ... what could it be for ?

I do not believe thats factory, looks like someone had a light rack on it an one point then took it off.

That looks the size of your standard NMO type antenna mount.

Given the position on the roof, that would be a safe bet.

edit: No, it is not "Factory"

Ron

i remember back, way back, when we used to drill huge holes like that in cars to mount antenas for "car phones". (yes there was once mobil car phones mounted in a car). that might be one that got removed and plugged. i have an 89 waggy that still has the wireing and window antena for a car mobil phone. that would be the optimum spot for the antena install back then, since you can get access from the interior light. you should have seen us drill these holes in brand new mercedes and all sorts of high end cars. im still kinda laughing about it.

Is the vehicle a former national parks/police unit? I agree with Ron, that looks like a hole for an NMO mount. You can get ones that require a much smaller hole nowadays but back in the day you were poking a pretty big hole in your roof.

Looks like dark green paint so I would bet on some sort of forest service or ranger vehicle.

It always amazes me that someone goes to the effort to remove an NMO mount instead of just putting a cap on it. By the way, it's a plug and not a grommet. Around here, it's the easiest way to identify an ex-police vehicle because they will have four or five plugs on the roof.