Knot for looping leader but to fly line

[bucko]

The nail knot is what I use to connect the fly line to 50 pd mono. At the leader end of the 50 pd mono I use a Perfection Loop. A second Perfection Loop is used to connect to 8 or 9 feet of 20 pd mono. I avoid letting the nail knot and leader get into my Guides.

[jeffsod]

If the fly line has a loop then use a perfection loop at the leader fly line connection. Most commercial leaders come with this knot. A surgeon's loop could be used but the leader will not be straight off the fly line using that knot.