The Luxaflex Blinds Slimline Venetian Spring Loaded Hold Down Plunge and Bung Combo is designed to go in the Bottom Rail to hold the blind down and not get blown in if there is a window open. If you are installing this into a Luxaflex blind that was bought without it you will need to shorten the bottom rail for this to fit. And you will need to buy the Pin and Bung as well to go in the other end.