Fibula?

[le Cavalier Invisible]

Ok, my Roman misc. objects knowledge is a bit rusty.. :oops:

The object in the attachment was described to me as fibula, but after some cleaning, I think it might be something else. (I included one "before" pic, and one really bad X-ray pic, the other ones are the object as it is right now.)
It might be in B&C's RME, but I can't really remember.. :roll:
I´m treating this object for school, it was dug up in Tongeren (BE) a few years ago.

Could somebody please enlighten me?
Sources would be greatly appreciated!

Thanks in advance guys!