It looks like flat plate 12x10 Scott #424a. I am pretty sure I might be wrong. Any opinions on this one please.
Hi, John... your Ohio precancel is a Scott $498 perf 11 (11x11)
If you haven't already, I would strongly suggest obtaining a good
perforation gauge, and a copy of Scott US Specialized Catalog,
both of which can be obtained inexpensively on ebay.
As an additional note... if you're on Facebook, I can recommend two
excellent precancel groups which you can join with very knowledgeable people.