Size A is what most use for fresh water poles. There are a few exceptions to the rule. If you are building a sturgeon rod you know the kind with a butt 1/2 -3/4 of a inch and the tip the size of a pencil then you want to use size D. on of course is correct the finish helps to strethen the wrap. If you are building a stanard fly, spinning, or casting rod then Size A is it anything else, size D