I am wondering what good a stinger with no ball on it is?
Some agriculture trailers slide over that and a large pin with smaller keeper pin is used to keep large pin from bouncing out. I used to pull tandem cotton trailers or peanut trailers that hooked up like that.
To add to Oklahomabassin's post, time was pickup bumpers had 1 or 3 holes in the bumper in that thinner part of the bumper where the license plate is located.
A trailer would have a clevis type hitch similar to the image below. Note the two holes lined up, one above the other.
Once the trailer hitch was located with the top part of the clevis above the hole in the pickup's bumper and the lower part under the bumper, then the hitch pin (similar to the pin below) is inserted through the three holes. Hitch pins were made with different sized shafts so that one could use one close to the size of the three holes so that there was little "play" in the hitch and pin.