Rolling works bizarrely in Savage Worlds. Essentially, everything above a 4 succeeds, which is why 1d12 is the cap as that is already overkill. 1d4-1 is essentially for untrained skills. There's way more to it though, and I highly suggest looking up the rulebook!

I prefer something along the lines of Savage Worlds. You start with 1d4-1 then 1d4, 1d6, 1d8, 1d10, and finally 1d12. Technically, you could homebrew it to go to 2d6, 3d4, etc, if you wanted.