Just to add to travlerajm's answer. Based on what I've read on this thread, the cross should be a thick gauge, low stiffness and slippery (low COF). This is where ZX is so good. As it is slippery with low stiffness. You can view the COF of a string here - http://twu.tennis-warehouse.com/learning_center/COFreporter.php You can view the stiffness of a string here - http://twu.tennis-warehouse.com/learning_center/stringfinder/stringfinder.php. In the dropdown menu, sort by power.