Use to attach leader butt to fly line or to attach backing to fly line.
Take a 1″ to 2″ long hollow plastic or metal tube of small diameter (a piece of drinking straw will do) and lay it next to the end of fly line. Lay butt end of leader on top of tube in the opposite direction with about 6″ to 8″ of leader butt extending beyond end of tube.
Hold fly line, tube, and tag end of leader together in left hand. Grasp tag end of leader and wrap over itself, tube, and end of fly line in five or six closely spaced turns. Move from left to right toward end of fly line and hold wraps in place with thumb and forefinger of left hand. We’ve eliminated hand from picture to show wraps clearly.
Pass the leader butt through the tube so the end passes back under the turns you’ve just made. Pull the ends of the monofilament in opposite directions, tightening them on top of the tube.
Carefully slip the tube out, holding the wraps securely in place.
Pull tag end of leader until the turns under your hand begin to tighten. Lubricate knot and pull tight on both ends of leader. Pliers or hemostat can be used to hold the tag end of leader.
Trim tag ends of fly line and monofilament close to knot.