The first variable affix can be any of the three desired affixes from the 14 possible affixes available, which means it’s (3/14)
The second variable affix can be any of the two remaining desired affixes from the 13 remaining available affixes, so (2/13)
The third variable affix has can must be the one remaining desired affix from the 12 remaining available affixes, so (1/12)
So, doesn’t that make it…
(3/14) * (2/13) * (1/12) * 100% = 6/2184 (as opposed to 1/2184) = 0.278%
It’s still tiny though and the chance of getting a primal element / chc / chd / cdr / socket amulet feels like it might take longer than the heat death of the universe.