I have listed the uses for the knot below the video.
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Improved Clinch Knot
Line-to-Hook Knot. Good all around knot for fly fishing.
Uni-Knot
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This is the most important knot to learn. The Uni Knot (or Duncan Loop) can be used as a Line-to-Hook, Line-to-Line, Leader-to-Fly Line, or Backing-to-Fly Reel knot. I prefer to use the uni knot when I am using heavier tippets (2x+) for steelhead and salmon and with light tippets (6x-8x). You can use this knot as a replacement for a nail knot.
Line-to-Line Uni Knot
I prefer this knot for attaching two lengths of of heavy leader.
Surgeons Knot
Line-to-Line Knot. This is the easiest line to line knot to learn. The Surgeons Knot is also stronger than the bllod knot, easier to tie, and uses less leader than the Uni Knot.