⎯ 3/ 8, nps 1/ 2, nps 3/ 4, nps 1, nps 11/ 4, nps 11/ 2, nps 2, nps 21/ 2, nps 3, and nps 4. 301 moved permanently. per en 1092- 1, flanges ansi 16. benefits of the inner ring. 34 as do the following api standards for other valve types: api standard 594