Your question has been answered dozens of times on this forum. First you need to scan some threads and learn about this site. Once that is done then come back and ask some details that may need more explanation. I would suggest that you use one word descriptions and use the search feature above. Search words like Pressurized or Differences. This will provide so much info you will really start to understand the members on this forum, there is so much information here
Here are a couple threads that came up that may help to answer, good luck and happy reading
http://www.337skymaster.com/messages...ead.php?t=2190
http://www.337skymaster.com/messages...ht=Pressurized
http://www.337skymaster.com/messages...ht=Pressurized
http://www.337skymaster.com/messages...ht=Pressurized