This is one of the most effective ways of joining two sections of leader together, whether they are of the same diameter or of different diameters. What you have is two individual grinner knots that slide down and butt up against each other to create the ‘double’ join. Also referred to as the double Uni knot.
This knot is perfect to attach a hooklength to the mainline
Double your mainline to create a large loop
Fold the loop over to form another loop.
Pass the first loop at least twice through the second loop.
Moisten the knot with saliva and pull it tight. Trim the knot and you are away.
Follow the same process with your hooklength and pass it through.
This knot has many uses for the angler.
It can be used to link hooklength to mainline, it can be used to join a paternoster link to a mainline, and it can even be used to join mono to braid.
Many angler's use this knot to link their pole mainline to the hooklength, especially when fishing delicate rigs, because it is far more direct than the more commonly used loop to loop technique.
Lay the two lines you wish to tie alongside each other.
Form a substantial loop using the two lines
Ensure the two lengths of line are together and thread the pair of tags ends through the loop three times.
Moisten the knot with saliva or water and slowly pull it tight. Trim off the tag ends accordingly to either create a straight profile when joining a mainline to hooklength, or cut the tag ends to create a paternoster link for legering purposes.