The surgeon's knot
The surgeon's knot is the quickest way to join two lines or tippet sections of similar diameter. You lay the two lines side by side and tie a double overhand knot through them both. It is fast, strong and easy to tie with cold hands, which is why fly anglers reach for it to add tippet or build a leader at the water.
Lay the end of your leader and the end of the new tippet side by side, pointing in opposite directions, with a good overlap, around 15 cm, so you have plenty to work with. From here you treat the two lines as one.
Take the doubled-over pair and form a simple loop with them both together, as if tying an overhand knot in a single thick line. Keep the loop open and roomy for the next step.
Pass the new tippet and the tag end of the leader through the loop together, then pass them through the same loop a second time. Two passes makes it a double surgeon's knot, which is the strong version, so do not stop at one. Keep the wraps loose for now.
Wet the knot. Take all four strands, both standing lines and both tag ends, and pull them slowly apart so the knot draws down into a neat barrel. Pulling all four together keeps it seating square and stops it crossing over. Pull it firm, check it has bedded down evenly, then trim the two tag ends close.
Four steps. Each one is a panel in the diagram above. Wet it before you pull it tight.
What it ties
Two lines together, joined end to end. It is the knot for adding a length of tippet to your leader, or joining two leader sections, when the two lines are a similar diameter. You lay the two lines side by side with an overlap and tie a double overhand knot through both, treating them as one. It is quick, it holds close to the full strength of the line, and it copes with a moderate difference in diameter, which is why it is the everyday line-join in fly fishing. It is at its best in mono and fluorocarbon, the lines you use for leaders and tippet. For a neater, slimmer join of two lines of the same diameter you might prefer a blood knot, but the surgeon's is faster and easier in the cold.
When to use it
Use the surgeon's knot any time you need to join two lines of similar diameter quickly, which in fly fishing means adding tippet to a leader or joining leader sections as you build the leader down to the fly. It is the knot to know when your fingers are cold, the light is going, or you just want to be fishing again fast, because it is about as simple as a line-join gets. Keep a good overlap so you have room to pass the ends through twice. The one thing to watch is that you pass both ends through the loop twice, not once; a single pass is weaker. If you want a flatter, tidier join and have the time, a blood knot sits sleeker, but for speed the surgeon's wins.
Strength and tips
Tied well the surgeon's knot holds close to the full strength of the line, which is impressive for how quick it is. The thing that makes or breaks it is the double pass: pass both ends through the loop twice, not once, because the single-pass version is noticeably weaker. Wet it before you seat it, then pull all four strands apart together, both standing lines and both tags, so the knot draws down square and the wraps do not jump over each other. Keep a generous overlap so you are not fighting for line. It copes with a moderate difference in diameter, but for two lines of very different thickness it loses grip. For a flatter, neater join of two similar lines, the blood knot is the tidier choice; the surgeon's is the faster one.
1Wet it
Wet every knot before you pull it tight. A dry knot drags against itself as it closes and the friction heat weakens the line.
2Seat it slowly
Draw it down slowly and evenly, then trim the tag end close, leaving a stub of a millimetre or two so it cannot slip back through.
3Test it
Pull the finished knot firmly against your hand or the rod before you fish it. Better it fails now than on the take.
Rigs that use it
The surgeon's knot builds and repairs the leaders on the fly rigs. It joins leader sections and adds fresh tippet on the dry-fly rig, the nymph rig and the streamer rig, the quick line-join you use streamside as the leader shortens through the day. It is the fast everyday join across all three.
Surgeon's knot questions
Joining two lines or tippet sections of similar diameter, quickly. In fly fishing it is the knot for adding tippet to a leader or joining leader sections. You lay the two lines side by side and tie a double overhand knot through both. It is fast, strong and easy to tie with cold hands.
Twice. Passing both ends through the loop two times makes the double surgeon's knot, which is the strong, reliable version. A single pass is weaker. Keep a good overlap so you have room for two passes, wet it, then pull all four strands apart to seat it.
Use a surgeon's knot when you want speed and ease, especially with cold hands or fading light. Use a blood knot when you want a flatter, neater join and have a little more time. Both join two lines of similar diameter; the surgeon's is faster, the blood knot is sleeker.