aluminum works, but i have found over the years working with aluminum recessed hex plugs, that all hex wrenches are not created equal. and when the wrench doesn't fit EXACT, the hex strips, or rounds out, causing me lots of grief removing them after the fact. i prefer steel or brass for just this reason alone. stainless plugs are good, but you have to make sure the threads are coated with something that will prevent galling. if you don't, same grief applys. just my experience and preference.