I think that Mark nailed this one. Many farmers had a blacksmith shop on the farm, we did, & a lot of hardware on yokes, single trees, wagons & about any thing else iron was made in the shop…These could have been used in the first yoke shown..A LOT of these items were fit thru the hole & then swaged or hammered to mushroom the end as bolts & nuts were scarce around many old subsistence farms…
The size is about correct for this application……Donnie