Fly Fishing Knots: Doubled Fly Line Loop Video
The Doubled Fly Line Loop is used for making a permanent loop in either end of fly line. It's best in fly lines bigger than 7 weight as it is bulkier than a nail knot.
See detailed instructions below the video:
How to Tie the Doubled Fly Line Loop
2. Tie a second speed nail knot in the same manner one inch from the end of the fly line loop. Trim the ends.