Strap and pin
A device for keeping a book closed and preventing the distortion of its shape. The strap-and-pin mechanism, known from before 1200, consists of a small metal plate with a raised pin placed at the centre of one of the boards; a long leather strap attached to the other board ends in a pierced metal tab designed to slot onto the corresponding pin. The use of two strap-and-pin mechanisms is characteristic of bindings from the fourteenth century on in England and slightly earlier on the Continent. The pin was on the lower board in England and occasionally in France, but it was usually on the upper board on the Continent. Strap-and-pin mechanisms continued to be used into the early modern period. See also clasp.
Michelle Brown, Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).