[Hairyogre]

Do you mean an option with:
max durability <=
max durability >=
?

That would do it =). AFAIK, the game only has very set levels of max durability, ie 40, 70, etc. So unless you want to future-proof the mod or use <= / >= for consistency, just a "max durability =" condition should do the trick.

There is a skill that increases max durability, i believe :P

Is there? I guess that's not really a surprise (you can't go by me, my highest couple of crafter skills are in the 40s). Besides, the "=" wouldn't work well as the approach for 70s and 80s are the same AFAIK. You need >=70 AND <=80 to meet that criteria without layering tons of duplicate skills. So yeah, the flexibility of your standard approach would work best =).