How to join two lines
Tie main line to a leader so the join is strong, slim, and passes through the rod guides without a hitch.
Last reviewed 26 September 2026 · Editorial policy
What this skill is for
The join between your main line and a leader is the most common failure point in the whole rig. Done well, it is nearly as strong as the line itself; done badly, heat from a dry knot or a bulky shape quietly destroys it on the first cast or the first run.
What you need
- Main line
- Leader material
- Line clippers
- Patience and a wet finger
Step by step
- 01
Match the diameters
A leader similar to, or a step thinner than, the main line joins cleanly. Tying a very thick line to a very thin one wastes strength whatever knot you use.
- 02
Use a compact double knot
Uni-to-uni — a uni knot in each line, the two loops interlocked and pulled together — is the everyday choice for monofilament, braid and fluorocarbon. For braid to a thin leader, a slim ali or a fg-style knot passes the guides better.
- 03
Moisten, then tighten slowly
Wet the knot with saliva or water and pull the two standing ends together steadily. Heat is what kills knots; a dry, yanked tightening can cost a third of the line's strength.
- 04
Trim the tag ends close
Cut both tags short and neat so nothing flapping catches a fish's attention or the spool.
- 05
Pull it and watch it
Load the join firmly with your hands. It should hold without slipping and stay straight. If it deforms or slides, cut it out and retie — do not fish it and hope.
- 06
Retie after abuse
Any join that has been dragged over rocks, passed through a snag, or fought a big fish is a fresh join now. Cut it back and tie again.
Where it goes wrong
- Tightening dry and heating the line.
- Joining very different diameters and expecting full strength.
- Leaving long tag ends that tangle in the spool and scare fish.
- Reusing a join that has already passed through the guides under load.
Related guides
Common questions
What do I need for join two lines?
Main line, Leader material, Line clippers, Patience and a wet finger. Nothing specialist beyond that — if a step needs something extra it is listed in the guide itself.
What is the most common mistake with join two lines?
Tightening dry and heating the line.
How do I know join two lines is done correctly?
The knot is small and neat, passes silently through the guides, and holds a hard hand pull without creeping.