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"...What are known as French joints are generally used for library books because they allow a thicker piece of leather to be used for covering than would be possible or desirable with an ordinary joint, and they also prevent the concentration of the creasing of the leather at one point. By permission, the illustrations in the Royal Society of Arts' Report showing the advantages of a French joint over an ordinary joint are given herein (see Fig. 22). The upper illustration of a section of an ordinary joint with the board open shows that the creasing of the leather is concentrated on one line ; the lower illustration of a French joint shows how this creasing is distributed over a greater surface, and so enables sufficient flexibility to be obtained with much thicker leather than can be used with an ordinary joint. It will be observed that a French joint is obtained by keeping the boards a short distance (about 1/8 in.)