How to Tie a Perfection Loop
In fly fishing, a Perfection Loop is most often used at the butt end of a tapered leader. It allows the leader to be securely attached, via loop-to-loop connection, to a loop at the end of the fly line. Although not as streamlined as the more traditional nail knot, the loop-to-loop connection does make it quick and easy to change leaders right on the water.
For the curious, here are two more versions of tying the Perfection Loop on MidCurrent.