T6-series aircraft-grade aluminum!
T6 is not a series, but a heat treatment. You have to be more specific. 6000 is a series, and 6061 or 6063, etc. is the metal grade. So one grade of aircraft aluminum would be 6061-t6, specifying the grade and the heat treatment, though I dont have a clue if that's what's used in these scopes, as I'm not involved with the company at all.