The fitting size is 2 inches.
Yes, this product is made of both zinc and aluminum.
Tina, the 42" aluminum Anode Rod will fit your hot water tank, If it's too long you can always cut of the bottom link, If necessary.
No, the diameter is not 0.75".
Yes, this anode contains zinc.
I had the same problem several months ago. Your current anode rode is probably for city water, you being on a well is different, well water has a bacteria in it, (which is harmless), but once heated will ignite the bacteria, which causes the rotten egg smell. Change your anode rode to a aluminum/zinc anode rode and this will solve your problem. Changing the rod is very easy. Hope this helps.
The magnesium rod is fine for city water, but if you are on well water then use the aluminum/zinc rod and the water will not smell like rotten egges.