1. Always assume that you have the most common variety, not the rarest variety.
2. Measuring a stamp is the least helpful criteria for IDing a W/F stamp.
3. Please do a SCF forum search on '596' for many, many threads where the likelihood of finding one is discussed.
4. Please read on learning how to ID the printing types of this era (flat plate, rotary, offset) http://www.stampsmarter.com/learnin...methods.html
5. Please read this article (especially Appendix 1)http://stampsmarter.com/learning/ID...arities.html