Aircraft-Grade Aluminium (6061)

6061-T6 is the alloy GMI machines from. It's lighter than zinc, stronger per unit weight, machines to tighter tolerances, anodizes cleanly, and holds sharp threads for years. Cheap grinders use zinc die-castings — heavier feel, but soft threads that strip, teeth that dull, and coatings that flake. 6061 is the difference between a tool and a toy.