Bakuha can turn objects into weapons so long as the object he is changing into a weapon is the exact weight of the weapon he is creating and as long as it is made of the components of the weapon. For example, he can turn small amounts of steel into a kunai or large amounts of steel into a katana, but he cannot make a katana out of wood. Another example; he cannot turn a kunai into a katana due to Renkinjutsu's equivalent exchange laws, though he can turn an enemy kunai into a dagger or even one of his own.