Why are rotary press stamps wider or longer than their flat plate counterparts?
Rotary plates are curved around a cylinder, while flat plates are of course “flat”. It is this curving that increases the length or width of the stamp design. The stamp designs were wider if the direction of the curve was in the sidewise direction, for example on the 170-subject plates used to make sidewise, i.e. horizontal, coil stamps (coil stamps connected to their left and right neighbors). The stamp designs were longer if the direction of the curve was in the lengthwise (endwise) direction, for example on the 150-subject plates used to make endwise, i.e. vertical, coil stamps (coil stamps connected to their top and bottom neighbors) . This knowledge is of paramount importance to philatelists who wish to separate varieties of stamps. For U.S. collectors, many of the rarest 20th century stamps are examples of these wider or longer rotary press stamps given the perf 11 perforations of the flat plate stamps. Knowledge of this “stretching” is also important in separating coil varieties
