D3 is a ancient nerd term for a theoretical three sided dice. To simulate it many many manufacturers make a six sided dice with two 1 , two 3 and two 3 faces. The chances of rolling a one are 1/3 . It is not that difficult people.
But that’s
not what GW are asking you to do.
That’s where the confusion is coming in.
It’s
very clear that they’re asking you to roll a
D6, a physical die they provided with six sides sequentially numbered 1 to 6 and to translate the result rolled into, usually*, inches of movement.
- 1-2 = 1”
- 3-4 = 2”
- 5-6 = 3”
Then occasionally they tack on an extra rule for when you roll a 1 on your D6, giving a 1 in 6 chance of activating that rule.
That’s
before you translate the numbers actually rolled on your actual physical die into anything else.
It has
absolutely nothing to do with actual or theoretical three sided dice or six sided ones with 1-3 duplicated, else they would’ve provided one. Or asked you to use the firepower dice, which they don’t. They ask you to use a D6.
The rules might also call for a D3, but an actual three-sided dice is not necessary.
P41 Underhive Rulebook.
Because you’re rolling a D6!
I never see this bad faith interpretation applied to a D66; someone saying they rolled a sixty-six sided die and rolled a 5, therefore not getting any results as they start at 11. It’s
very clear they’re asking us to roll two D6s one for tens and another for units. It’s just they never wrote the “D3” shorthand clearly enough for some people.
*I’ve not been through every instance of “D3” in the library of books. Regardless they’re asking you to translate the results of a traditional D6 into whatever and regard a 1 on the D6 as the thing that activates another rule. It could just as easily be “a natural 4” on the “”D3””.