If you look at the Catan number-circles that you use use to mark the tiles with their roll, they have a set of dots on them - 6 and 8 have 5 dots, while 2 and 1

If you look at the Catan number-circles that you use use to mark the tiles with their roll, they have a set of dots on them - 6 and 8 have 5 dots, while 2 and 12 have 1 dot. The dot is the numerator over 36 of its probability. Likewise, if you use the Traders and Barbarians dice-deck, the same thing applies - there are 5X as many 6s and 8s in the deck as there are 2s and 12s.