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Attach the cut 2-foot 2x6 treads to the marked stringers. For each tread, align its top edge with the top horizontal line previously marked on the stringer. Ensure the center of the tread (marked in the previous step) is aligned with the pilot hole on the stringer. Drive a single 3-inch screw through the pilot hole into the tread, ensuring it is flush. This initial single screw per side will hold the tread in place temporarily, allowing for minor adjustments later during the leveling process. Repeat this process for all treads.