Especially conceived for its application in the preparation of catalogues or any other practical situation in which similar features are required, whenever it is necessary to extract its sheets one by one, along with the addition of other new ones, and based on a set of rings as means of securing for the sheets to be bound, said rings being connected to a support plate fixed on the corresponding spine of the folder, complemented by a sliding plate able to occupy a position for locking of the rings or for their release, in order to be able to add or extract the said sheets, the invention is centred on the fact that the rings (1, 1' and 1") have a configuration tending towards a semi-circular outline, and are fitted in securing elements (2) forming modules or blocks for fitting on the actual support plate (6) for fastening to the spine of the folder.