asymmetrical three-line tools

Source reference: 

Pickwoad, The structures and materials... (2014)

Nicholas Pickwoad (2014), "The structures and materials of commercial bookbindings in the Arcadian Library", in The Arcadian Library: Bindings and Provenance, Studies in the Arcadian Library, Oxford, Oxford University Press, pp. 1-78.

Additional reference: 
p. 285

Used as preferred label for