This is an antique wood treadle sewing machine top. A Damascus sewing machine came out of this.
The Opening is a little less than 7" front to back and 14 5/8" wide. Cabinet measures 34 1/4" wide x 19 1/2" front to back. With the top extended, it measures 49 1/2" long. There are no pins, but would measure 9 1/4" between the pins. Pic #4 is the bottom side of the top. There are 2 screws on the backside that hold the piece of wood in place--otherwise it would fall through. Ink pen is pointing to one of the screws.
Very old piece. Last pic shows a crack in the wood.