5 wt for trout,smallys,large mouth,small lakers. 7tor 8 wt for steelhead,lakers,pike,muskys,9-10 for atlantic salmon and the bigger stuff, you get the message. A switch line in the weight class that's on your rod erring on the heavy side, will let the rod load and unload much better than using a conventional w.f., or s.h. line. Switch and spey rods need line designed for them if you want to get the best performance out of them. Check to what your rod likes with other fisherman who have the same setup, it will save you from experimenting and saves you money. sorry this was late ive been busy.