Bead and board (hollow|) wainscoting - 1/16" thick x 3 1/2" wide x 24" long. The spacing is 1/4". One piece.
The detail lines run horizontally along the 24" of the sheet. It can be cut to the height you want for the wainscoting. For example, wainscoting 3" high on the wall will need a 3" cut from the 24", turn a quarter turn and install on the wall. Repeat the 3" cut and place the pieces side by side on the wall. Top with wainscot trim.