Above, my duckbill pliers. From right to left: unknown, unknown, Pexto KS 6015, Utica KS 6015, unknown, unknown.
Below, the variations on jaw and hinge geometry:
It's interesting that the model numbers are the Utica and Pexto pliers are identical. Cooper Tools (now the Apex Tool Group) ended up owning both companies in the late 1960's, and perhaps the same pliers were offered under the two brand names for a while. The owernship progression for both companies went as follows:
Pexto ► Billings & Spencer ► Crescent-Niagara ► Cooper Tools ► Apex Tool Group
Utica ► Kelsey-Hayes ► Triangle Corporation ► Cooper Tools ► Apex Tool Group