Is this keg stainless or aluminum?

[WVShiner]

Hello all,
My brother has an old keg. I took the valve out this weekend and cleaned it up, but I wanted to be sure it's stainless and not aluminum before using it. Problem is, I can't find stainless or 304 or 316 or anything that I'm familiar with that would say for sure it's SS. The biggest clue is this string:

16/18 15.5 79 4 D

I would assume the 16/18 is gauge and 15.5 is capacity but the rest I don't know.

Any help is appreciated.

[Tater]

try a search that's been answered several times.