Thread the rod to the plate, screw up the threaded rods and plate with M10 nut and M10 washer at both end. You don’t have to tighten it because you need to adjust the distance between the front and rear plate later when you assemble the side panel.
Tips: the Y-axis must be a rectangle, that is the rods on both side should be parallel, so is the front and back plate. Otherwise it will cause obstruction for the belt later. You can use a Digital Caliper to measure.