This March Brown Nymph imitation is tied on a barbless AHREX FW501 in a size 12.
If you are fishing in the morning or cannot see any signs of a March Brown hatch, then nymphs are the way to go, in the early season it is sometimes more productive to use a brighter nymph, than the drab more imitative ones.
Always keep in mind how deep and how fast the water is when nymphing in the early season, that will tell you how heavy a nymph you need to use. All you need to remember when fishing nymphs in the early season is that you need to be near (or on) the bottom, if you're not getting snagged up every so often, you're not fishing deep enough.
This fly is only available in a size 12.