Douglas Fir 3″ x 6″ for a boardwalk for ATV’s and Dirt Bikes. We S1S this material (surface 1 side) so the deck is perfectly flat. Install the surfaced side down, bandsawn side up for better traction. These pieces are all 6′ long. The handrails for the elevated portion are all 1-3/4″ x 6″ D fir.