J-Knot

Another good leader to main line knot of varying materials and diameters, the J-Knot is one that will require you cut a length of leader off before you tie it because the entire leader has to pass through the knot when tying it.

To Tie:
To start, pass the lines tag ends parallel to each other several inches. Now grabbing both lines, tie a simple overhand knot, pulling the entire leader through to complete the knot. Now, 2) grab the entire leader and the tag end of your main line and over lap them back into your half hitch again. Finally, 3) loop the leader and tag end through the knot once more and pull the leader and tag end completely through the knot. Moisten and pull all lines simultaneously to cinch the knot.

Notes:
You basically are weaving your leader in and out of a half hitch 3 times to lock the lines together. Depending on line diameter, this knot can be a little larger than some of the other line joining knots, so experiment and practice to see if the speed and size of the knot works for your applications.