Same is true of a TN from NH. The adjustable link ends are just to big for any of the locks I have found.
My solution was to get a 2 5/16" ball (10,000 lb) with a long shank. You can order then off the internet or perhaps at a local trailer shop. I think the one I have is 3" long and has enough space to go through the draw bar, and still leave enough thread for a washer and bolt.
I then just mount this on the large hole at the end of the fixed drawbar. Use an impact wrench to take it off and on as needed, since many ag implemets use just a pin and the ball must be removed.
Fred