Hey all. My name is Mark and I live in Arizona. I work in a hospital and as an emt for a search and rescue orginization. I have been using analogs for a few years. I recently switched to after a fairly invasive spinal cord surgery. I got suckered into a fifty-one trio by a mall vendor, and ordered a 510 manual from madvapes. I can barely stand it, it should arrive tomorrow and my fifty one trie died yesterday after a month. My one question is, what specifically makes a 510 a 510? I see there many different brands. Is it battery size or thread size?