Abstract: A sheet or plate (10) for use for example as a stiffening plate for a book cover comprises an adhesive layer (12) applied to a narrow zone extending along and adjacent to at least one end of the plate or sheet. The adhesive layer (12) is covered by a protective peel-off strip (13) having a free end portion (15). This free end portion is folded along a folding line (16), which defines an acute angle with the longitudinal axis of the protective strip, whereby the free end portion of the protective strip extends beyond said edge of the sheet so as to define an accessible gripping end. The plate or sheet (10) may be arranged and retained in abutting engagement with a second sheet or plate (21), such as a book cover. Now, the protective strip (13) may be removed by pulling the free end portion (15), whereby the sheets or plates may be interconnected.