I can't comment on the size of various threads, but I can offer a suggestion that may help with cutting the threads.
I'm assuming the brazing rod you're using is brass. If so, it has probably been work hardened during the manufacturing process. You can anneal it easily by heating it with a torch - a normal propane torch should get plenty hot enough, without the risk of melting anything. Once it's cooled off again, the brass will be much softer, which may halp with cutting the threads.
I'm assuming the brazing rod you're using is brass. If so, it has probably been work hardened during the manufacturing process. You can anneal it easily by heating it with a torch - a normal propane torch should get plenty hot enough, without the risk of melting anything. Once it's cooled off again, the brass will be much softer, which may halp with cutting the threads.