Abstract: The movable shutter device provided on a timepiece comprises stretchers in the form of oblong handles which are screwed onto a middle part of generally rectangular shape with flanks. The stretchers comprise a groove which is composed of a rectilinear portion followed on either side by a rounded portion, the latter giving on a groove which is formed by the surfaces of a protective plate connected to the back cover and by a flat portion of said back cover. The closed circuits formed by the grooves surround the middle part. The movable curtain formed by shutter axles which are interconnected on both sides by two rows of connecting links is slidable in said grooves by means of rollers made of rubies. In order to ensure that any intermediate position of the curtain between the two end positions is maintained, i.e.