The need to connect two lines is common in angling, typically when joining mainline to leader or tippet. And whether you chase tuna offshore, hunt bass on a southern pond, or trick trout with a dry fly, knowing how to connect two lines is essential.
But as any experienced angler can tell you, that point of connection is usually the weakest link of the chain connecting your reel to the fish.
More often than not, you can look for the culprit of a line failure at the mainline-leader connection.
That said, there are better and worse options for connecting two fishing lines, but most tend to be pretty specialized.
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Related: Top Fishing Lines By Type
When you’re thinking about how to connect two fishing lines, there are several questions that you need to answer to pick your best knot:
Let’s break that down to see why these answers are critical.
If you’re a fly angler who needs to connect your mainline to a leader or leader to tippet, you’re not overly concerned about the size of the knot you tie. Chances are, it’ll never come into contact with your rod’s guides, and whether it can cleanly pass through them just doesn’t matter that much.
Similarly, if you’re trolling for muskie or pelagic species like king mackerel, tuna, or shark, your mainline to leader connection needs to be rock solid, but it can be pretty big since casting isn’t the name of the game.
But if you’re a bass angler who’s throwing a length of fluorocarbon or monofilament leader to reduce visibility, a castable knot matters a lot. Ditto for pier and beach anglers who’ll be looking for long, efficient casts.
When you need the knot to slide through guides, size matters; choose a slim knot.
Material science and physics are everything when it comes to knots, a simple fact we’ve discussed before.
And while monofilament exhibits what engineers and scientists call a “high coefficient of friction,” meaning that it “bites” against itself and holds a knot like gum in your daughter’s hair, braid and fluorocarbon just can’t match that performance.
Practically, this means that a knot that holds in one line type may not hold well - or at all - in another.
And when you mix line types, which is common when we’re talking about leaders, you need to be pretty choosy about the knot that binds two different materials.
Always choose a knot that works in the line types you’re connecting.
When you tie two lines of the same diameter, knots tend to work pretty well. But when those diameters vary greatly, otherwise strong knots can fail.
That’s because the larger line can’t always create enough bite with the smaller one it’s paired with, though there are knots that are superior to others in this respect.
Now, you might think the answer is just to pair two equal diameter lines (or lines that are pretty close), and that’s typically easy when you’re talking about mono to fluoro connections.
But when you’re using braided mainline, that’s not going to happen, and you need a connection that can handle that difference in size without letting go.
Be careful about braid to mono/fluoro connections and choose a knot that can handle different line diameters.
The FG Knot is a favorite of saltwater anglers who chase pelagic species, and it’s the go-to knot of pros and weekend fishermen alike.
Why do they like the FG knot so much?
Those are simply huge advantages, and when you add to that the FG knot doesn’t require a bobbin to tie, you can easily see why it’s so popular.
Unfortunately, it’s not an easy knot to tie well, and it’s as slow as they come.
The J Knot is the darling of fly anglers the world over, and there’s simply no better connection you can make between fly leader and tippet.
What’s so special about the J knot?
The Double Uni is a great knot for connecting lines of different materials and diameters, and it’s popular in both fresh- and saltwater applications. While not great for casting, most anglers find that their leader lengths allow them to keep this knot out of their guides.
Why do people like the Double Uni?
The downside of the Double Uni is that it doesn’t cast particularly well, and it will bang through your guides, reducing casting distance and possibly compromising the knot over time.
Keep your leader short and the knot out of your guides.
There are advantages and disadvantages to every knot, and there are situations in which they all shine.
If you need a smooth casting, super-strong connection, and you don’t care how long it takes to tie, the FG is worthy of its unmentionable name. But the Double Uni is much, much faster, and with short leaders, it works really well.
Neither is a good idea for joining leader to tippet (or tippet to tippet), and the J knot is probably the way to go.
Select the right knot for your lines and situation, and you’ll be amazed at the results.