What Is This New South Wales Queen Victoria Stamp?

According to my understanding of the Scott catalog this stamp is supposed to be imperf. Has it been privately perfed? It is 11 1/2 at top and bottom and 11 along the sides. Stamp is yellow green with watermark 55. Thank you all for any ideas.

Look at Scott 35-37, 43, 54 and 63. Those are the Perf and watermark varieties of this stamp.

These stamps were originally imperforated,the stamp you have was reprinted from the original plate and the perforation was added when the new perforating machine was introduced.

Rob

It's Scott #63h

There is a natural variance across the perforating line so they're rounded up to 12.

This used to be expressed perf. 11½-12

Hope this helps!

Okay, now I'm confused. It's early for me and I've only been up an hour and a half, but for this I don't think all my coffee would work. I read the threads for learning until I get my catalog in the mail.
Bluehearse said the stamp was 11 1/2 x 11. So, I understand rounding up the halves but, rounding a whole number? Please explain more in detail if you don't mind.
What I mean is - is the 63h a perf 12 x 12?

Scott 63h is perf. 12x11

There is a natural variance over the perforating line. For this stamp, the top of some stamps might measure 11½, some 12, some might measure somewhere in between. It was a rather inexact science all those years ago!

The 'perf 12' is described by Stanley Gibbons as 11½, 12. There were actually two perforating machines used until October, 1902, one measuring 11½ per 2cm (178 holes over 30cm), another measuring 11.8 (173 holes per 30cm). SG determined that it was too difficult to tell the difference on single stamps and amalgamated the two to the 11½, 12 measure. The machine gauging 11½ was converted in October 1902 to make the 'OS / NSW' punctures.

This info from ACSC "The Postage Dues" 2nd ed, 2014 pp 10/46-47.