Family Life What is ZZ R 765? What is ZZ R 765? A-A-59588, formally known as ZZ-R-765, is a defense and aerospace specification. This material is compliant with Federal specification A-A-59588 2A for high temperature resistance in 40, 50, 60, 70, 80 shore A durometer hardness values. Related Posts:How much does an Aerospace Engineer make right out of college?Whats harder Shore A or Shore D?How do you measure an o-ring durometer?How many years does it take to study aerospace?