The purpose of this report is to provide guidelines for specifying O-rings that would be considered suitable for testing when writing O-ring material specifications. There are many tests that have been developed to characterize rubber O-rings. Many of these tests are independent of the size of the O-ring being tested. However, there are some tests, specifically, stress/strain properties, that are a function of the O-rings size. The purpose of this report is to provide guidelines for specifying O-rings that would be considered suitable for testing when writing O-ring material specifications.