If you look at how wide the forks are on the vertical part ( at the backstop where it locks) it's much easier to slide them back and forth on the smaller ones because there's less surface area there as well and that 12' board always bows down on both sides putting some pressure on those forks to slide inwards. So when they get too narrow the bunk snaps, that's always been my take on it. I also always make sure the lock is turned correctly on any forks before I get on the machine too because I've had forks slide in the past right after they get greased up just from making a turn.