You are probably like, hey Warlord Games does not make that model, and you would be correct. The Onager is a RAFM model with a converted plastic Warlord Games crew.
So when you have tons of these miniatures, and need a siege weapon, this is what you do.
And you can see I converted the guy holding the rock, one of his hands, with the other being from a spare Bucinator or Cornicen.
The guy holding the shaft was a converted Pilum throwing arm.
The extra rocks are leftover greenstuff.
So there you have a Roman Onager. I think the scale of the two different manufacturer lines worked out pretty good. The RAFM if I remember right is 25mm, and the Warlord Games miniatures are actually 25 mm, not the 28mm that Warlord erroneously markets them as being, a major screw up on their part in my opinion.