First Crack At This. 498 545 Or ?

I am new to this. I have been carrying around a shoebox full of stamps I found in one of our old houses when we did some remodeling. I believe this is 11 gauge. If you only measure the colored part of the stamp I believe it is 19mm wide and 22mm long but I used a wooden ruler. I ordered a better gauge tool. Based on the back I think it is flat plate. Any other advice? This is the first post for me. So far I think it is likely a 498 or a 545. I did read someone's advice to think you have a more general stamp as a rule and work from there. Therefore, I am guessing a 498.

Perf 12, Scott 405.

Agree with rogdcam, perf 12. It has been pointed out numerous times on this forum that counting perfs is no substitute for using a perforation gauge and can yield the wrong answer (the perf "size" is the number of perforations within a distance of 2cm=20mm). However, if you don't have a perf gauge, your stamp is an excellent example of when you can sometimes successfully "count" perfs. The WF (Washington-Franklin) design generally measures between 18mm & 19mm in the horizontal direction. Add in some of the margin on either side of the stamp, and you have your 20mm. So count the perfs all the way across the stamp, margins included. On your stamp, add the almost complete perf on the bottom left corner of your stamp to get to 12. Of course, this quick mental calculation doesn't work as well in the vertical direction … the design generally runs 22-23cm vertically. Note that as long as you are working with a whole number, this "counting" process works fairly well. But if you have a fractional number, say 10.5, then counting becomes a bit more problematic. But for the WFs, this only arises with Scott 536 and some of the coils.

I agree, it's perf 12.