I need to find a particlur type of connector

[csziggy]

I've got some vintage cast iron horse and wagon pieces. Various wagons - grocery, Coca Cola, ladder wagon, fire tank wago, and a beer wagon.

Most are in good to very good condition but I just bought two that while in good condition, need some work. There is a piece, maybe a screw that holds a pair of horses to the double yoke that helps them pull the wagon. Since on the horses that are already attached you only see the brass ends, I am not sure if they are similar to Chicago screw or a rivet. The brass ends are flat on both ends, with no place to use a screw.

I only have two pairs of horses without this attachment, the beer wagon horses need a piece about 3 1/2" and the ladder wagon horses need one only about 2 1/4"

If I knew what this was called, I might could find what I need

By the way, these pieces are vintage, not true antique. They are probably between 40 and 60 years old. They are fairly crudely made, but overall they make a nice collection so I'd love to have the whole set ready to display.