Mine is 1", and you probably will find a Zinc anode (not Aluminum) unless you look carefully
Also, as usual, Maine Sail has proper instructions for anode install. I started following them and actually saw a big difference in anode consumption (which is good).
Basically: Use a wire brush on a drill to brighten up the insides of the anode (wear leather gloves!), then use 220 paper to brighten up shaft where anode will go, then tuf-gel the stainless bolts before attaching the anode. Finally, tap the anode onto the shaft with a light blow on each side to seat it before final tighten.