I would say that is mainly length. Rods (the translation of which to spanish more or less would equate that of wands) are longer. They need not at all to be nor thin nor slender, anchor rods of big diameter -and with heads- are sometimes used. Sometimes rods are exposed in significant length to the air, bolts more rarely so. And rods normally will have significant length without threads. In any case, bolts and rods are used when referring to anchors unto concrete.
As I understand these words in our part of the world, a Bolt is something that has a head formed onto it at one end, while a Tie Rod has both ends threaded for nuts.
