Bend a loop in the tag end of the heavier line and hold between the thumb and forefinger of the left hand.
Slip the tag end of the lighter line under your left thumb and pinch it tightly against the heavier strands of the loop. Wrap the first turn of the lighter line over itself and continue wrapping towards the round end of the loop. Take at least 12 turns with the lighter line around the three strands.
Insert the tag end of the lighter line through the end of the loop at the bottom. It must enter and leave the loop on the same side.
With the thumb and forefinger of the left hand, slide the coils of lighter line towards the end of the loop, and stop 1/8 of an inch from the end of the loop. Using pliers, pull the tag end of the lighter line tight to keep the coils from slipping off the loop.
With your left hand still holding the heavier line, pull on the standing part of the lighter line. Pull the tag end of the lighter line and the standing part a second time. Pull the standing part of the heavy mono and the standing part of the light line.
Trim both tag ends.