American Standard Chain are covered by ISO 606, ANSI B29.1. The pitch sizes covered by this standard are 1/4-to-3-inch pitch. American standard chains have a smaller pin diameter than their European standard equivalent. Wear resistance is therefore reduced when compared with European standard chains with the one exception, 5/8-inch pitch. In this case the pin and bus diameter are larger in American standard chain.
American standard chains are normally referred to under the ANSI standard numbering system for example a ½ inch pitch duplex chain would be, ANSI 40-2.