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Apply a generous bead of construction adhesive (such as Gorilla Glue Construction Adhesive) to the top edges of the stringers and along the front edge of the riser where the new tread will sit. The adhesive acts as both a strong bond and a lubricant, helping the tread slide into place. Carefully lower each custom-cut tread into its position, ensuring the rabbet joint on the back of the tread slides into the dado on the riser below it. Push the tread firmly against the riser and down onto the stringers. Use a hammer to gently tap the tread into its final, tight position if necessary. Finally, use a finish nail gun with 2 1/2-inch (8-penny) finish nails to secure the treads, driving nails through the top surface into the stringers. This combination of adhesive and nails ensures a strong, squeak-free installation.