Does this ceiling electrical box look fan-rated?

I'm replacing an old light fixture with a ceiling fan, but I'm not sure if the electric box is fan-rated. Here's what the box looks like.

It's not like others I've seen. It has a big threaded nipple coming out of the top, which makes me think it's probably attached to something solid. But I don't see any screws going out to the side, and only one going up through the top which is attached to the ground wire. What do you guys think? I suppose I could crawl up into the attic to check from the top side, but I wanted to see if any of y'all could tell from the picture. Thanks!

Submitted January 25, 2015 at 02:59AM by codyrushing http://ift.tt/1EfUuig