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Insert the rollers into the top and bottom brackets and also into the tubes on each hinge. If a roller has two tubes, always place it in the tube farthest from the door. Next, assemble the jam brackets and flag brackets to the vertical track according to the instructions in your manual. With a helper supporting the door panels in place, carefully remove the temporary nails you toenailed in place on one side. Slide the vertical track over the rollers, ensuring all rollers are fully seated in the hinges, leaving approximately a half-inch gap between the edge of the door and the track. Do not force the track, as this could cause the door to bind. Pre-drill at each lag screw position and loosely attach the flag bracket and track brackets. The tops of both vertical tracks must be level with each other; verify this by measuring from the top of the door to the top of the bracket on both sides. Check that the tracks are plumb, then fully tighten the lag screws.