I would not recommend using those with exposed metal as amplifier output posts. Too risky when it comes to the possibility of short-circuits.
from ApexJr you could sell the extras and recoup your expenses easily. (I did this some years ago. While they did not sell like hotcakes back then, the local DIY community has become much more active since).
Agreed on the exposed ones, probably not a good plan... he has no info on what they are made of.
I had previously bought binding posts from Yebo, which were copper when I drilled through.When I bought again they were what looked like brass... but I don't think it was brass, looked like some cheap & nasty other material, and the gold plating... well it looked strangely un-gold. So I want to but something I know is decent, info there is a bit low to go through the effort of an import.