| Technically, a 50 Class reel was originally designed to fish 50lb, a 30 30lb and a 20 20lb. On the east coast that still holds true more than on the west coast, but with the advent of super braids and increased drag capacity you are seeing reels pushed 2-3x their original designations, with 50 class reels easily fishing 130lb line with 40+lbs of drag. These Class reels have been produced from size 6 to 130.
To make it somewhat confusing, in the last 25 years or so we have seen small saltwater reels with similar 12,16,20,30,40 and 50 size classifications, such as a Saltist 50. These smaller reels are often fished with the same test line as their model, 20lb on a 20, 50lb on a 50 and so on, but not in the same application as a the larger Class reel.
As far as the 4/0, 6/0 and so, reels produced for saltwater fishing early on were given size ratings of 1/0 - 14/0, and even large in some rare cases. It is believed the /0 stood for Ocean, but the true origin of the /0 is not really known. The reel size and line capacity varied somewhat by manufacturer, but as a whole was fairly standard. Depending on the actual application, many will use the reel size to determine the line rating. 40lb on a 4/0, 60lb on a 6/0, 80lb on a 9/0 and so on. | 
I will admit this will be so very basic to you guys. So I will aplogogize in advance. My problem is with understanding what is meant by a 50 class reel vs. a 30 class vs. a 20 class vs. a 4/0 reel and 6/0. Where did these designations come from and what are they used for.
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