Not required Item Variants

How would I import this item with its three variants?

It can’t be just sizes, because then I’d have two times 6’’.
So I would need something like “named sizes”?
Or a second attribute. But this second attribute would be empty for the first two variants and as of now the attributes for variants can’t be empty.

What to do?

I would use two attributes but come up with a name. Something like:

  • Length (4", 6")
  • Shock (“None”, “Coil-over”)