554c Or 595

I'm not sure of the following stamp. I'm wondering if it's a 554c or a 595. It's very difficult for me to measure and also difficult to line up the stamp with the Specialty Gauge on the scanner. If you look at the upper left corner, it lines up OK at that point. It then touches the heavy line to the right, meaning it's a rotary press, right? or not? Also, notice it does NOT touch the bottom heavy line. In other words, it's wider than a 554 but not taller. Scott's says a 595 is 19 3/4 x 22 1/4. Does a 595 need to be both wide and tall? I thought just one direction since the plate is only curved in one direction. Finally, I have read that coils (554c) can also be a bit wider. Please help! Thanks.

(Edit Note: I meant booklet, not coil... thanks, chasa)

595's need to be wide only... the BOOKLETS are often a lttle wider too, so they can be hard to identify.
This looks like a 554 booklet single to me, but impossible to tell from the scan. Does the reverse have tell-tale signs on red ink specks?

Looks to me that according to the instructions, it appears to be rotary printing (595) since the design touches the heavy line. However, it may not be a 595 which is 19.75mm by 22.25mm. I have read that some stamps over time or during soaking expand and do not return to the original size. A Weiss certificate may give you an accurate ID. Is it worth the money for a certificate? That is up to you but several sites I have seen say a certificate is required.

Here's a scan of the front and one of the back. Yes, it's got red ink on the back. What does that mean?

Can you have a used stamp certified? Either way the odds of it being a booklet pane is MUCH greater due to the straight edge.

this is definitely 554 based on the reverse

What causes the ink to be on the back of the stamp?

When US stamps were printed on flat plate presses [obsolete for many years], the sheets were stacked when they were not completely dried. This is before putting on the gum. 99+% of the flat plate stamps have them. Rotary press stamps do not have them because the machinery does the printing, gumming, perforating, and cutting basically in one process from continuous rolls of paper.

While I'm disappointed a bit about it not being a 595, I happy to get the education from the more experienced collectors here. Thanks for all the info, chasa. By the way, do you know what caused the stamps printed from flat plates to widen? And is this widening only in the booklets?

The significant widening occurs on the ROTARY press stamps [SC 578/579/594/595/596/613] when the plate [originally laid down flat on unhardened steel] is fitted to the roller. The stretch can be vertically or horizontally which are different Scott numbers.
Flat plate stamps can show slight differences in design size when paper is fed to the press 90degrees out of 'normal' when printing booklet sheets and the paper shrinks on a different bias. These differences are never as pronounced as with the rotary stretch. I have often been fooled by this when searching for SC595's especially on cover when the reverse is not easily available.

According to the gauge it's at least 19.5 mm wide. What I'm hearing you say is, the flat plates won't make a stamp that wide. With the ink on the back, it seems we have two "definitive" signs that shouldn't be on the same stamp. Quigngt says that time or soaking may affect the width. Can you tell I want this to be a 595?