The Ideal Pet Flexible Flap Window Inserts are designed for both cats and dogs. There are four pet opening sizes to choose from. All models are available only in white. These inserts have an approx. 5 inch adjustment range, allowing for the possibility of moving the unit from one window to another, as long as your window widths fall within the same given range. These units are designed to be inserted into the track that your window glides up and down in. The sash window closes down to the unit, providing the stability. There are no locking mechanisms that come with these units, however, most customer will use a brace-bar or stick above the top window so that it cannot be opened.