The uni knot and the double uni knot are both popular knots used to tie braided fishing line. The uni knot is a single knot used to attach the line to a hook or swivel, while the double uni knot is used to join two lines together. The double uni knot is made by tying two uni knots, one with each line, and then joining them together. The double uni knot is stronger than the uni knot and is ideal for attaching leaders to braided line.