Abstract: Book nipping apparatus having first and second pairs of jaws adapted to apply nipping pressure on a stack of signatures. The first pair of jaws is structured to press the signature stack together adjacent the signatures' back or spine edge in a straight spine edge configuration, and the second pair of jaws is structured to press the signature stack together adjacent the signatures' front edge in a curved, or deformed, front edge configuration. The first and second jaw apparatus functions to prevent the center signatures in the stack from tending to slide or squirt out of book alignment with the outside signatures in the stack when the entire stack is exposed to the full nipping pressure.