Have you tried it on another battery setup (a friends perhaps)?
If it won't screw on your battery, there has to be one side that has buggered up threads. I can't count the number of times in my life I thought the threads were good, but in reality one side was messed up.
One the downfalls of copper, is that it is a relativity soft metal and the female 510 threads can get messed up easily.
