A few days ago, Steve Jelf posted a comment on square nuts. I'd like to add more information to the bolt part of it. I'm including a few photos of the bolt they used in '13, of which there are two different designs, both slotted. The early '13s used two short bolts on each side which attached to the TOP rail of the frame. Around March, they created long bolts which went all the way down and attached under the bottom rail, and also held the engine pans on. There is a long one and a short one, but are still slotted.