What is it fir and what dies it do.

A sacrificial anode is usually made from magnesium, aluminum, and zinc. Magnesium has the most nutral electropotential of the three.
Boats use copper sometimes.

There is no data on this at all!

https://www.google.com/search?q=8MV50-2+replacement+anode

..

Magnesium or aluminum?
http://waterheatertimer.org/Replace-anode-rod.html

Gene

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

1) Ask question on pro water heater site run by foremost anode expert, and also ask about the power anode rod that works electrically instead of chemically and will not have repeated problem you describe:
http://www.thetankatwaterheaterrescue.com/forums/forum3/

2) More info about anodes:
http://waterheatertimer.org/Replace-anode-rod.html#power

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

There are two types magnesium anode.
1) Hex-head that screws into separate port on top of tank, and comes either 44" long or 12" sausage links.
2) Combo-anode that connects to Hot water nipple, and comes in solid or combo.

Contact guys at following link to purchase anodes
http://www.waterheaterrescue.com/pages/WHRpages/English/OrderPages/XCart/sales-through-XCart.html

General instructions and types of anodes
http://waterheatertimer.org/Replace-anode-rod.html

Rheem 'preferred parts'
http://waterheatertimer.org/pdf/2011_Rheem-anode-rods.pdf
Purpose of resistorized anode is supposedly so magnesium performs as well as aluminum.
Rheem however had 'resistorized elements' years ago, and that turned out to be promotional gimmick so people would buy rheem-brand products.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You are installing a combo anode rod that replaces hot water outlet nipple. This means you will have 2 anode rods, which doubles the anode capacity of tank, which can cause extended life of water heater, assuming that both anodes are inspected each 2-5 years.

Sounds like a heat trap insert is in the way.
Look at parts sheet that comes with product manual.
Pull insert out since it will cause clogs.
Same insert is on cold side nipple.

I want you to contact the Tank forum since they are anode experts:
http://www.thetankatwaterheaterrescue.com/forums/forum3/
Tank will recommend magnesium anode and not aluminum.

My understanding is that Rheem water heaters are made so only Rheem brand anodes fit their tanks. While other companies use generic anodes that are sold at any plumbing supply, and also sold at Tank website.

You can configure pipes to make heat traps that save save $2-4 per year on gas water heater operation.
http://waterheatertimer.org/images/Heat-trap-install-900.jpg
http://waterheatertimer.org/How-to-maintain-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Anodes are located on top of water heater.
There are no hard fast rules for location, either by model number or brand.
Most times the manual is likewise vague.
1) There is hex head visible on top of tank.
2) Hex head is located under a plastic cover
3) Hex head is located under metal top, so remove screws holding top, and lift top off to view hex head
4) Anode is connected to hot water nipple.
5) With 9-12-15-and lifetime tanks, you can have 2 anode rods, and each has to be made of same material to work properly. Usually magnesium-aluminum instead of aluminum.
But if you inspect and change anodes frequently to prolong life of tank, then one is as good as the next.
http://waterheatertimer.org/Replace-anode-rod.html

Open following links shows Rheem anode rods
http://waterheatertimer.org/pdf/Rheem-Ruud-anode-rods.pdf
http://waterheatertimer.org/pdf/Rheem-Ruud-water-heater-parts-guide.pdf
Tech resistor anode rod has resistor added to prolong life of anode.
You can cut rod off to fit size of tank. You want anode 5-6" from tank bottom so sediment build-up doesn't reach anode.
Anodes are standard 1-1/16" hex head.
http://waterheatertimer.org/images/Water-heater-anode-006-200.jpg
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

Add a comment with your experience so others with same-similar problem can benefit.

Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

I would have to go along with your brother on this one. The aluminum anode rod is by far the cheapest way to go. Other options include extensive filtration,ozone treatment and acid treatment.
The aluminum anode rod is much cheaper and I would recommend you change it yearly at least. Good luck and thank you.

Anode rods are aluminum -or- magnesium and aluminum

http://www.waterheaterrescue.com/pages/WHRpages/English/Longevity/water-heater-anodes.html

http://waterheatertimer.org/Replace-anode-rod.html

Hello EDAN I believe it is 1 1/16" socket.I had 1/2" drive & extention bar as it very TIGHT & hard to turn the rod nut.