Huck bolts are used in place of rivets or bolts to permanently connect parts. They are common in the railroad industry being used on car structural components, grab irons and ladders, and even joint bars in the tracks. In the this application, the Huck bolts would be designed to shear in a specific manner allowing a controlled failure. I believe the idea was that at a certain level the draft gear attachment would partially fail allowing some of the energy to be absorbed by its collapse/compression underneath the car. I'm not sure what they did further on the ends, at one time there was talk about the end of the cars being allowed to crumple but not telescope. Without vestibules, not sure where the crumple would happen but it wouldn't have been into a normal seating area.