public double ArrowSizePoints {get; set;}

{
  //Note: Must be on QueuedTask.Run

  //Build geometry
  List<Coordinate2D> plCoords = new List<Coordinate2D>();
  plCoords.Add(new Coordinate2D(1, 8.5));
  plCoords.Add(new Coordinate2D(1.66, 9));
  plCoords.Add(new Coordinate2D(2.33, 8.1));
  plCoords.Add(new Coordinate2D(3, 8.5));
  Polyline linePl = PolylineBuilderEx.CreatePolyline(plCoords);

  //Set up the arrow info
  var arrowInfo = new ArrowInfo()
  {
    ArrowHeadKey = ArrowInfo.DefaultArrowHeadKeys[1],
    ArrowOnBothEnds = true,
    ArrowSizePoints = 30,
    LineWidthPoints = 15
  };

  var graphic = GraphicFactory.Instance.CreateArrowGraphic(linePl, arrowInfo);

  //Make an element to add to GraphicsLayer or Layout
  //var ge = ElementFactory.Instance.CreateGraphicElement(
  //  layout, graphic, "Arrow Line", false);
}

{
  //Note: Must be on QueuedTask.Run(() => { ...

  //Build geometry
  List<Coordinate2D> plCoords = new List<Coordinate2D>();
  plCoords.Add(new Coordinate2D(1, 8.5));
  plCoords.Add(new Coordinate2D(1.66, 9));
  plCoords.Add(new Coordinate2D(2.33, 8.1));
  plCoords.Add(new Coordinate2D(3, 8.5));
  Polyline linePl = PolylineBuilderEx.CreatePolyline(plCoords);

  var arrowInfo = new ArrowInfo()
  {
    ArrowHeadKey = ArrowInfo.DefaultArrowHeadKeys[8],
    ArrowOnBothEnds = true,
    ArrowSizePoints = 24,
    LineWidthPoints = 12
  };

  //Create and add element to layout
  GraphicElement lineElm = ElementFactory.Instance.CreateArrowGraphicElement(
    layout, linePl, arrowInfo, "Arrow Line", true,
                              new ElementInfo() { Rotation = 15.0 });
  //lineElm.SetName("New Line");
}