The "Knot-in-Knot" is so simple that it's uninspiring at first glance, and you need to have tested it a number of times and with some nice fish to trust it. I've been using it almost exclusively for a long time now when fishing with hard lures. Not only is it disconcertingly quick to use, but it has never failed me... I recommend you give it a try!
Its biggest advantage is undoubtedly that it can be used with very large diameters of fluorocarbon, which is often quite complicated with other knots.
For greater visibility, the knot is made from 50/100 fluorocarbon.

- Step 1: Tie a simple knot in your fluorocarbon 2 or 3 cm from the end.

- Step 2: Tighten this knot as tightly as possible. Its role is to act as a stop and prevent the final knot from slipping.

- Step 3: Re-tie a single knot higher up on your fluorocarbon, about 3 or 4 cm away from the first one. This time, don't tighten it - it should be about 1 cm in diameter.

- Step 4: Slide your lure onto the fluorocarbon so that it sits between the two knots.

- Step 5: Pass the first knot (the tight one) through the second.

Step 6:
- Moisten your knot with saliva.
- Tighten the second knot firmly and slide the free strand so that the knots abut.
- Trim the excess 2-3 mm from the knot.
Your node is now complete.
Advantages :
- Extremely fast and simple
- Gives your hard lure plenty of freedom
- Suitable for all fluorocarbon diameters sizes, even the largest
Disadvantage :
- You'll need to spend some time testing and using it before you can really trust it, as it seems so simplistic...