Abstract: A binding mechanism for the binding of perforated papers, has at least two elastically flexible tangs (5,6). These tangs (5,6) are arranged standing upright on the top side of a flat support strip (1). Their ends are releaseably connected with extension pieces (9,10). In order that the tangs (5,6) with their extension pieces (9,10) can be formed into ring arcs whose size is adaptable between a minimum and a maximum, to the bound paper stack height, the support strip (1) made of plastic has passages (7,8) into which the extension pieces (9,10) can be releaseably and lockingly inserted to different depths. The extension pieces (9,10) consist of separate, likewise flexible, rod or tongue like elements which have at least the same or a greater length than the tangs (5,6). The passages may be provided at their insertion-side ends with a detention edge or with a lock tooth, and the extension pieces with a lock tooth system.