~~~ bondholder and the Treasury after purchase -- nothing.

Also, with the Series-I Bonds (purchased at face), the Treasurey permitted buyers to purchase up to three $10,000 bonds per year (...and looked the other way if you bought a few more $10,000 bonds over the $30,000 for that year) but, today, your max purchase is only $10,00 per year (at least it was a couple years ago).