The Duo blends variables of single fins and twin fins and produces a smooth, deep drive unlike anything else I have ridden.Ā  I have been refining these fins since 2015, with the concept of creating greater hold and release than a single fin with the speed of a twin.Ā  If youā€™re building a board, the twin center boxes are set 7.0ā€¯ apart and 7.25ā€¯ up from the tail with 4 degrees of cant and no toe.Ā  You can also use a single DUO with small side bites for a very drivey 2+1 set.