Measure the width of your stair runner. Stair runners are generally 27 or 32 inches wide. Select carpet rods that are the appropriate size for your runner. Your carpet rods should be at least 4 inches longer than the stair runner is wide if they are 1/2 inch in diameter, 5 inches longer if the carpet rod is 5/8 inch in diameter and 6 inches longer if the carpet rod is 3/4 inch in diameter.
Place the mounting brackets on each side of the carpet runner, making certain that they are centered on the runner. The carpet rod is installed at the intersection of the bottom of a riser and the back of a stair tread. Make a mark at each screw hole in the carpet rod bracket. One screw goes into the stair tread and one into the riser.
Remove the mounting brackets and drill a 1/16-inch pilot hole at each mark you made.
Confirm that your carpet rod will fit between the brackets. If it is too long, trim it with a hacksaw or a jigsaw fitted with a blade for cutting metal.
Slide the mounting brackets over the ends of the carpet rod and attach the finials.
Put the mounting brackets back in place and use the screws provided to affix them to the stair.