Fastenings are used to hold a book shut when it is not in use. They can take a variety of forms and be made from many different materials, but their essential function is secure one board or cover to the other across the fore-edge of the bookblock and often the head and tail edges as well. Fastenings were in use from the earliest times, but after the introduction of printing and, more particularly, the near universal use of paper-leaved textblocks, their use gradually became more and more decorative and status-related (ie. for liturgical or ceremonial use), unless they are found on books which were intended to be carried about, in which case they retain a primarily functional purpose. Fastenings may also be found on enclosures.
Where there are three fastenings on the fore-edge of a book, the central fastening is the one which is found between the upper and lower fastenings.
Where there are two or three fastenings on the fore-edge of a book, the upper fastening is the one which is closer to the head edge.
Where there are two or three fastenings on the fore-edge of a book, the lower fastening is the one which is closer to the tail edge.
Disks or devices of other shape having holes or a shank by which they are sewn or secured to an article and that are used as fasteners by passing through a buttonhole or loop or a trimming.
The Arts and Architecture Thesaurus Online, The Getty Research Institute.
Short lengths of ribbon, braided cord, parchment, alum-tawed skin, etc., passed through a ring at the end of clasps to make it easier to pull them off catchplates or pins.
Fastenings in which either loops of cord, alum-tawed skin, tanned skin, etc. are attached to one side of a binding and are used to hold the book shut by being looped over a knot, bead, toggle, etc. attached to the other side, or loops from each side are secured by passing a stylus through them along the edge.
Clasp fastenings consist of two parts: one a catchplate or pin located on one board or cover of a book, and the other a hook or ring on the opposing board or cover which catches on the catchplate or pin on the other side. The hook or ring may be attached to the board by means of a clasp strap or a hinge plate.
Metal fittings attached to the fore-edges of both boards of a binding with rings at their ends which allow a stylus to be passed through them from head to tail, thus holding the book shut.