I'm assembling my CNC Router Parts PRO4896 (it's actually a foot longer). The instructions say to be sure to butt the two ground ends of the linear rails together (for the long axis), and the drawing shows one end to have a bevel, and the other to be flat. But mine have no bevel, so I can't really tell which end is precision-ground. Are both ends ground? Is there a way to tell? Thanks!