Hi Shweta,
In order to achieve this you need to set the stroke style width to zero and configure the ArrowStrokeStyle - the following code shows how to achieve this:
NRectangularCallout callout = new NRectangularCallout();
callout.Text = "Some
Label";
callout.UseAutomaticSize = true;
callout.Anchor = new NDataPointAnchor(bar, 1, System.Drawing.ContentAlignment.MiddleCenter, System.Drawing.StringAlignment.Center);
callout.ArrowLength = new NLength(40);
callout.ArrowBasePercent = 0;
callout.TextStyle.TextFormat = TextFormat.XML;
callout.FillStyle.SetTransparencyPercent(100);
callout.StrokeStyle.Width = new NLength(0);
callout.ArrowStrokeStyle = new NStrokeStyle(1, Color.Black);
Let us know if you have any questions.
Best Regards,
Nevron Support Team