A peg from an ancient book (possibly pre-Mongol time), that is, part of the fastener.
In addition, it became clear that until the 17th century the pegs were without holes for their fitting. Most likely, a small hole was drilled in a wooden wrapping around the book and the peg was driven in.
The clasp of an ancient book consists of two parts: a peg and the loop itself

Weight:7,3 gr Diameter:39,3 mm