An Eifel Geared Plierench, likely dating from 1941. Josiah Carberry Collection.
A Plierench is a hand tool that combines the parallel jaws of a wrench with the compressive handle-and-jaw action of a pair of pliers. Several designs exist, with the jaws and handles interacting via gearing or linkages. In some designs the relative position of the handles and the jaws is adjustable, whereas in others it is fixed.
Also features a wire cutter and screwdriver/pry tool.
Pros
The benefits of the plierench stem from the jaws and their interelationship with the handles. The jaws are generally smooth, lacking the teeth seen on many pliers, and so are less likely to damage the work piece. The use of the handles to change the distance between the jaws eliminates the need to size the jaws in a separate step, before using the tool - sizing is done as the tool is applied. Further, it means that the strength of the tools grip is variable, allowing the tool to easily grip delicate items or firmly grip robust ones.
Cons
The jaws also represent a design weakness, however, as their smoothness means that as the plierench is turned (to tighten a nut, for instance), the work piece pushes the jaws apart. Thus, a plierench cannot apply large amounts of torque. Similarly, its gripping power is related to the strength of the user.