secondary boards

Source reference: 

Sharpe, The Earliest Bindings... (1999)

John Lawrence Sharpe (1999), “The Earliest Bindings with Wooden Board Covers: The Coptic Contribution to Binding Construction”, in International Conference on Conservation and Restoration of Archival and Library Materials. Erice 22nd-29th April 1996, edited by Carlo Federici and Paola Munafò, vol. 2, Palermo: Palumbo Editore, pp. 455–478.

Additional reference: 
p. 462

Used as preferred label for