public double ArrowSizePoints {get; set;}

//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(
//  container, graphic, "Arrow Line", false);

//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(
  container, linePl, arrowInfo, "Arrow Line", true, 
                            new ElementInfo() { Rotation = 15.0 });
//lineElm.SetName("New Line");