The thread size is what's called 1/2" pipe thread, and it's the shorter of the two rod lengths. The longer one is for suburban water heaters. The Atwood water heater tanks are aluminum, so an anode isn't really needed, unless you have bad water. I installed one in 2012 when we bought our TT, and a year later, it came out looking like new. I haven't used one since.
If you're going to "regret it in the morning", sleep until noon.
2012 Jay Flight 19RD
2016 Ford F150 XLT 2X4 SC 3.5L Eco Max Tow
2010 Tundra TRD DBL Cab (Traded)
2 new fluffy Corgis, Bayley and Stanley