To specify the size of all major ticks you should use the MajorTickRelativeWidth and MajorTickRelativeHeight properties of the respective Scale object. You can use the MinorTickRelativeWidth and MinorTickRelativeHeight properties to change the size of the minor ticks or the MiddleTickRelativeWidth and MiddleTickRelativeHeight properties to change the size of the middle ticks respectively. The tick's size is relative to the cell size of the scale.