The inside couple (always!) makes an arch and steps
forward as the outside
couple ducks through
the arch into the center of the square.
The outfacing couple then does an automatic
California
Twirl to complete the movement.
If the outside couple is taller
than the inside couple, it is
appropriate to "fake" the
arch - let go, then reconnect
after the other couple has
passed by.
For more detail on Dive Thru , click here: