Fit the decorating bag with tip 21 and fill 1/2 full with medium consistency icing. Hold the decorating bag 45° angle at 4:30 (7:30); the tip should be lightly touching the surface. Using a steady, even pressure, move the tip in a gentle sideways "S" curve. Stop pressure and pull tip away.
Insert tip under the bottom curve of the "S" shape.
Squeeze the bag with steady pressure as you pull down, then lift the tip. Move up and over the tail of the "S" as you continue to squeeze and form a hook.
Keep spacing as even as possible and "S" curves uniform in thickness, length and overall size. Be sure to tuck the tip into the bottom curve of the previous "S" before you begin squeezing, to insure the clean, continuous look of a rope.