Early Oxen Yoke

This is the only Oxen yoke that I have ever seen with an adjustable metal bar for the bows. Every other one that I saw, the bows were made from wood. These are hand forged wrought iron. By the looks of the ring in the center of the yoke, it shows that this tool was used a long time. That ring is 7/8 " in diameter.
Instead of OX Bow Pins to hold the metal hoops, (or, bows), this yoke uses keyed pins.
A friend of mine, who is well knowledgeable of period woods and their origins, told me that the wood beam is made from Slippery Elm. Upon visiting the Liberty Bell Memorial in Philadelphia, I was told that this is the same wood that holds the Liberty Bell. ...hotairfan