Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

French joint

A free-swinging joint produced by setting the board a slight distance (approximately 1/8 to 1/4 inch, depending on the size of the book) away from the backing shoulder. This type of joint allows thicker covering material to be used, while still allowing the covers to open easily. The French joint is one of the more notable characteristics of library binding. Also called "open joint." See also: CLOSED JOINT (94 , 335 )