For crafting (and possible gathering) equipment it seems the left side has a fairly high chance to give tier IV(75%~ or higher), and an uncommon chance at tier III.
On the other hand accessories and tools seem to have an incredibly low chance at tier IV, and even a moderate chance to give tier II. (yes, tier II materias, even from level 60-59 tools)
So for anyone looking to save gil and spiritbond their own materias I would advise to only spirit bond the leftside items. Tools and accessories arent good for tier IVs at all.
