I've always been wary of using the term "duplicator" to describe small presses. By their very nature, all printing presses duplicate things, so the term doesn't offer much in the way of class distinction or describe a machine's capability. Nonetheless, small format offset machines have suffered a bit of an identity crisis since their introduction to the market in the late 1930s.
Sheet size was frequently used to draw the line between the "duplicator" class offset machine and actual printing press. Any machine that could accommodate a sheet size over 10" x 15" fell into the printing press category, and below that resided the duplicators.
This was a little confusing, as small offset machines were originally built with common office form sheet sizes in mind, but those same press models were modified by manufacturers over the years to accommodate larger press sheet sizes and a greater variety of job work.
There were other features of smaller offset presses that were used by some to define the class. If instead of utilizing constant bearer pressure between cylinders, the machine featured spring loaded cylinders, the press was considered a duplicator or "small format" press. If the machine had fewer than three inking form rollers, the press was considered small format, and so on.
Printing historian Fred Roblin, in The November 1965 anniversary issue of The American Pressman, presented this name problem more eloquently and succinctly than is done here, and concluded that "regardless of the name ascribed to it, the duplicator is generally an offset press, embodying a feeder, a planographic plate, an indirect print on a rotary unit with inking and dampening systems, and a delivery."