That is the bell for a snap coupler. There should be a spring and hook that also go around the large pin that gose through the big hole. I believe the small bolt is a stop for the hook of the snap coupler. I"m still somewhat new to AC myself, but am so close to finishing my WD45 restoration soon, so don"t quote me on this.
You also may want to check out Agco parts book online. You can check out the parts books for free over there.