code: public void setCustomTickLabelFontSize(final double SIZE) {
          if (null == customTickLabelFontSize) {
              _customTickLabelFontSize = Helper.clamp(0.0, 72.0, SIZE);
              fireUpdateEvent(REDRAW_EVENT);
          } else {
              customTickLabelFontSize.set(SIZE);
          }
      }
docs: Defines the custom font size. The default font size is 18px at
  a size of 250px. This value will be used to calculate the current
  font size for the ticklabels when scaling.
  
  @param SIZE