What is NPT? - Hose Assembly Tips
Commonly used sizes include: 1/8, ¼, 3/8, ½, ¾, 1, 1 ¼, 1 ½, and 2 in. These can be found on pipes and fittings used by most U.S. suppliers. Sizes less than 1/8 in. are sometimes used for compressed air, while sizes more than 2 in. are less common, mainly because other joining methods are more often employed with these larger sizes.