Dryseal American National Standard Taper Pipe Threads are designed to provide additional protection against leakage because the root and crest heights of the threads have been adjusted to provide what is commonly referred to as an "interference" fit. Sealants are still recommended, but may not be required. ZrN coating to enhance life in applications where Aluminum is used. Special thread mill features have been used to make these perform better than standard general purpose tools when machining Aluminum.