A helical plastic coil is used for binding a collated book having a stack of pages with aligned holes along one edge of the book where a leading end of the filament is fed into a first hole at a first end of the book and the coil is rotated about its axis such that the leading end is threaded through the holes by entering each of the holes until the coil is threaded through all of the holes. The leading end of the coil is sheared by an anvil and blade so as to define a leading apex and a leading surface inclined rearwardly from the leading apex along the filament and across the filament. The leading apex is arranged such that, as the leading end enters each of the holes in turn, the leading apex is located on the leading end of the filament at a position thereon facing away from the trailing end of the coil and spaced from the end of the hole facing the first end of the book.