557 Rotary Or Something Else?

I initially identified this stamp as a 557 since it is perf 11 on all sides. If I searched the Scott catalog correctly, it is the only one with this design that is perf 11. 557 is marked as flat plate printing, however, when I measure it, it shows rotary (please see photos). The design on this stamp is definitely wider than that of 551-6 and 558-64.

Is this really a 557 or something else? Do some flat plate printed stamps such as this one have a design as wide as rotary printed ones? Thank you.

If perfs are 11x11 (and it looks like they are), then its 557. Looks like there is set-off on the back of the stamp, so flat plate. Measurements to determine rotary are approximations and you must compare stamps of the same issue (you are comparing apples and oranges). Just my opinion.

Check the perfs again, if rotary it should be 11x10.5, Scott 637. But I agree, the offset makes it a flat plate stamp.

Thanks for the responses. Perfs are definitely 11.0 on all four sides. I overlaid the stamp with another used 557, and the design measures 0.25mm wider. I guess that is not enough to matter?

Your alignment of the two stamps is offset slightly, as seen below, and if the stamps were aligned properly then the difference between the patient and the second stamp would be well within the bounds of paper variation for this issue. Remember, both stamps are old and we cannot know whether one or the other has been subject to environmental conditions, either at original printing or the successive years, that caused paper shrinkage or expansion.

Try matching the perforations tip to tip on the top or bottom and both sides. They will not match. Rotary press examples are a lighter, less saturated blue. The rotary press printing will have aligned top and bottom perforations, unlikely to occur on flat plate printings.

why do you measure the width? it is the height that will differentiate flat and rotary

Although unlikely if the stamp is used, rotary press coils have been reperforated top and bottom to resemble the more expensive perf 10 rotary press sheet stamps. The width of a flat plate sheet stamp is likely to be slightly narrower than a rotary press stamp because the paper was less damp at the time of printing. A rotary press horizontal coil will be much wider because plates must be bent enough to fit on the rotary press cylinder. (Two plates are required.) Vertical rotary press coils are very slightly taller than rotary press sheet stamps because the coil press cylinder is smaller.

Back to perforations. Why not compare with a stamp that exists only as the flat plate perf 11 or a rotary 11 x 10 1/2 or use a Kiusalas gauge?