Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

supported French joint

A modification of the FRENCH JOINT . It is used to impart additional support to the shoulders of large books. A thin board is glued to the book board; however, instead of stopping at the inside edge of the thicker board, it extends the exact distance of the intended gap between the board and the shoulder, i.e., the distance of the French joint. When the boards are attached, these thin boards press against the shoulders and help support them.