lineThickness : Number

Sets the thickness of the Scale Breaks lines in pixels.

var  chart =  new  CanvasJS.Chart("chartContainer",
{
 .
 .
 axisY: {
      scaleBreaks: {
	       lineThickness: 6,
	       .
	       .
      },
 .
 .
 },
 .
 . 
});
chart.render();