Anode rod - wrong part?

I ordered this anode rod from Amazon. Got it in yesterday, and went out to install it today. The old one is the one that originally came with the unit when we bought it in July '10. I got the old one out, and noticed that it has significantly less threaded length than the new one, as seen in this picture (yes, that is my blood - if there is a way to bust a knuckle or cut a finger while working, I'm notorious for finding it, and usually don't realize it until minutes later when I see the red mess I've made). I got the new one screwed in about halfway, and it's getting significantly more difficult to turn. I could keep going with a little elbow grease, but I thought I'd seek some opinions before I damage something other than my finger. Is this a suitable replacement?

I wouldn't force it - add the Teflon tape as Outbound mentioned, make it snug again and then test it under pressure.  I would pressurize the system, fill the WH, look for leaks, then turn the WH on and let it get up to temperature, then inspect for leaks again.

All good suggestions, I bough a deep socket and wrench at the local auto parts store and keep them in the camper as you should need it twice a year for winterizing and spring setup. You should only need a couple of wraps on the Teflon tape clean the threads, tighten and check you can always give it an extra little turn if it leaks. But trust me if you overdo it and hear a "crack" it's too late. I learned that the hard way in my heating and cooling days. :-)