You have to undo the sidesaddle screws so that separates into the back plate and front plate. There is a small nut that threads onto the screw that holds the ejector in place, and a bit of Loctite on these threads is a good idea. Assemble the back of the side saddle to your receiver with the longer ejector screw included and the screw that replaces the trigger group pin. Lastly, attach the front plate to the back plate.