Published Feb 24. 2014 - 7 years ago
Updated or edited May 6. 2018

Merging two fly lines

Splicing lines together using thread and glue can be replaced by another method if you are using coated lines. See how easy it is to weld lines togeteher using shrink tubes and a heater.


Practice on an old fly line or a cheap line. The first few times you might fail, but when you get the hang of it, its quit easy.

This is only a start-guide. There are many variants of making loops with shrink tubes. Make your own experiments.

Merging Two Lines

Below is a step-by-step guides showing how to make merge two lines. The method is universal for all coated fly lines and makes it possible to make you own WF-lines, smooth connections and more.

Step 1

- Insert your fly line into a piece of shrink tube af approx. 6-8 cm (2-3 inches).

Michael Sorensen

Step 2

- Heat the tips of the fly lines.

Michael Sorensen

Step 3

Remove the coating.

Michael Sorensen

Step 4

- Now the fly lines are ready to be merged.

Michael Sorensen

Step 5

- Sew the core from each fly line into the center of the coating of the other fly line..

Michael Sorensen

Step 6

- (optional) Before pulling the lines tight together, apply a bit of glue.

Michael Sorensen

Step 7

- Pull the fly lines tight together (before the glue dries out).

Michael Sorensen

Step 8

- Cut of the tag ends of the cores.

Michael Sorensen

Step 9

- Place the shrink tube over the merged position.

Michael Sorensen

Step 10

- Apply heat to merge. The coating should merge to the extra core inside.

Michael Sorensen

Step 11

- Remove the used shrink tube.

Michael Sorensen

Step 12

- You have now merged 2 fly lines.

Michael Sorensen

Tip 1:
This will not work on all fly lines!
It works better on floating lines than sinking and not on fly lines with a mono core.

Tip 2:
You can color code your lines by adding a small piece of coating in a different color under the shrink foil before welding. It requires some practice but the result is overwhelming.
Of course you can mark the line with markers before welding. However, this will fade over time.

This guide is made by Michael Sorensen from Innosoft, check out his fish condition calculator app here.

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