There never seems to be enough dividers that come with these trays, if you're even lucky enough to get any at all with your Stanley tool organizer trays. I've made dividers for both the small and the large trays. There's nothing special in printing them. I print on a Prusa MK3S with a 200um layer resolution. I've used PLA, TPU, PETG, ABS, and Nylon (though the Nylon wasn't very good quality.
The author hasn't provided the model origin yet.