double two sheets on
A method of sewing a book on tapes that is reputed
to give still greater strength than the ALL ALONG method.
Each section is sewn "two sheets on" with the
preceding section, resulting in each section being
sewn to the sections both above and below it. This
gives greater holding power because two threads
pass through each section; consequently, if one
thread breaks the other still holds the section.
Unless the first and last sections are sewn all
along, however, the weakness of this method is
that these sections, which receive the greatest
strain when the book is being
used—particularly the first section—are
not held very securely. In addition, not all of
the sections are held by the kettle stitches. (196 )