Hello. I've tried several searches trying to get an answer but just can't find one. I have a SH-15 that I want to swap the magnet out. In one of my many searches I found a seller on ebay that a lot of people use but there's a few things I'm not sure about when ordering. What size do I need? I've seen nominal 2.5"X0.50"X0.125" and 2.44"X0.492"X0.125 inches. What does nominal mean? Oriented or Unoriented. I've seen non-magnetized and magnetized. Help a newb out. Sorry if this a repeat question.