awspartb - look in you training material from your CWI test. I can't recall the exact book or section, but the topic is discussed, and the last number in the electorde number tells you if it is low hydrogen or not. If I had to say off the top of my head, I think the ending number of XXX4, XXX5, and XXX8 are the low hydrogen type. Again, that was a guess from memory so I'm not giving you the answer, which is what I'm not wanting to do anyway.