Tapered 1" of diameter for every 16" of length (or 62.5mm/m). American National Standard Taper Pipe Thread mills provide a piece part that forms a seal when the flanks of the part are mated. It is usually recommended that a sealant be used in these joints to prevent leakage of liquids, steam, hydraulic fluid or gases. 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.