Iron Rivets

Taken all the way down to base materials, one Iron Rivets is 2 crafting steps deep and needs 1 intermediate — Iron Ingot ×1 — which resolves to 1 distinct raw material totalling 3 units, plus 2 crystals.

That bill outweighs 3,373 of the 13,602 recipes tracked here and 410 of the 1,932 Blacksmith ones, and 4,464 recipes nest deeper.

Only 1 of those crystals go into the final step; the other 1 are burned by the intermediates, so the real crystal cost is 2 Fire Shard.

Every step is Blacksmith work, from a Lv 16 intermediate up to the Lv 18 finish, so one class covers the whole chain.

Its single raw material is gathered, and no spot for it is timed, so nothing in the tree waits on the Eorzean clock.

Iron Rivets is itself consumed by 48 further recipes, spanning seven of the eight crafting classes.