A:
It all depends on the species of the fish you are after. i assume that you have heard the terms 3 weight, 7, it goes up to 14 wts. this is the actual line weight, usually you would want a lighter weight line for more delicate siutations such as mountain trout fishing and as you progress your way to freswater and then to saltwater, you want a thicker and more durable line due to the increase in water size. the leader is just the same sizes range from 0-7x, 0 being the thicker and 7 being the smallest diameter where you tie your fly on. the rule of thumb is the smaller the fly, the bigger number on the leader your would want. bigger flies require thicker leaders. hope that answers your question.