As straightforward as the discussion on hubs might be, dies are the opposite.  The variations in dies can be thought of as deviations from the norm, starting with the original coin image and fanning out every time there is a discernible difference from the original intended form.  And then for more fun there are deviation from the original deviant.

For every coin there is obviously an obverse and reverse die that come together to stamp out a coin.  So you can have either a normal die, or a "deviant" die for each.

It is ultimately the combination of the dies that produce VAMs.  But the further delineation comes from deviations within a die, or die pair from the intended strike.

Rarity of an issue is definitely defined by the frequency of the appearance of coins with these combinations, and the experience of dedicated collectors.

The list on the right groups recognized VAMs by reverse die, which helps understand the designation system and differences in VAMs.  You can click on the VAMs or dies to see more detail.  What can be confusing is that the descriptive names are not the full description of the coin variances.

There are fewer choices for the reverse dies, eighteen rather than thirty-one, but your choices are no easier, especially when there are so many VAMs that rely on die a.

Reverse dies are separated just as obverse dies, but are designated be a letter rather than a number.  All 1881-O dollars are hub 3 and sub variety a.

You might see a designation of C3a, meaning hub C, sub type 3, die a.  There are 18 different dies for the reverse of the coins, designated as a through r.

Although you can identify dies and VAMs going down a reverse die decision path, we find it especially difficult because of the dominance of die a.  Die a dominates so much that you find yourself always looking to the obverse die for clarification and determination.

One of our detailed die studies involving die cracks delineates the different dies and can be accessed here.