I bought the truck used so i ordered those stops as well . I know on the train car there is a plank that the wheel stops clip onto to hold them in place but on the truck they have no way of staying secure. If you figure something out let us know .
those ridges are about 1/32" . As soon as the truck makes a sharp turn or hits the breaks to avoid the train barreling down the tracks the weight of the load shifts the stops and away goes the load