I did some research since my last post, and you are pretty close. 343C / 649F to anneal 5052. Don't know about Duralumin, but I bet its close. I figured I'ld pick up a 600F and 650F Tempilstik to leave in my tool box for future projects. The 600F to let me know when I am getting close and the 650F to let me know its ready. I read about using Sharpies, soap, etc, and I also read some reviews that they are not always right on the temperature. Could just be technique too.