Scroll down and there is a pic of a Bull Pull mounted to a round weigh pin on a J&M grain cart. Bull Pull might make an adapter for smaller diameter weigh pins but I know they did not make one big enough for mine (2 7/8" diameter).  J&M only made the adapter as a prototype (what is shown in the pic) and does not offer it any longer. Email me if you would like some more info about the adapter. 

https://talk.newagtalk.com/forums/thread-view.asp?tid=574653&posts=19&highlight=grain%20cart%20scales&highlightmode=1