Max is obsessed with tools (and trucks, tractors, trains, dinosaurs, dirt, water, talking, roaring...). Such a boy. Nature/nurture? Honestly, I think it's nature on this one. He's like a miniature version of my dad. (if Max was chubbier he'd be the spitting image of my father as a child)
Being such, Papa has made Max the best toy ever: A hammer board. He took a piece of scrap 1"x4" about 10" long and pounded five large nails into the board, leaving about 1" exposed (and no sharp bits of course), and numbered the nails 1-5. Then the two of them spent the next 45 minutes sitting on the deck working on the hammer board. Papa had his big hammer, Max had his toy hammer (that looks like a real one and we pretend is a real one, it even gets stored in Papa's tool box) and they had just a wonderful time.
Benefit: Enormous. Max can now count to five and he's not even two yet. :)