Lighting, Light Fixtures, Ceiling and Exhaust Fans - Is existing ceiling outlet box safe for fan?

I have removed a ceiling fan from the home I just bought. When running, even at the lowest speed, it wobbled. Now that I have the fan and mount removed, I see that if I push on the sides of the outlet box, it moves slightly.

I am concerned that the previous homeowner either installed the ceiling fan in a box meant for just a light fixture or they installed the ceiling fan box incorrectly.

How do I tell if this will be safe for my new fan? Pictures of the box are located here:

drop.io yahhzzb (http://drop.io/yahhzzb)

Thanks!

You should be fine...see those large nuts inside? Those use either a U shaped clamp over a framing member in the roof structure or around a mounting fixture between 2 rafters

And the mounting screws for the fan look much deeper than the typical ears in a box for just a light.

Thanks for your help! I got it installed!

That one of few ceiling fan box I used pretty often and they are good up about 60 lbs depending on the way it mounted.

Just make sure you used 10-24 thread opening { it far much stronger than 8-32 thread }

Merci,Marc