This Standard covers threaded malleable iron unions, classes 150, 250, and 300.It also contains provisions for using steel for NPS 1/8 unions. This Standard includes requirements for (a) design (b) pressure-temperature ratings (c) size (d) marking (e) materials (f) joints and seats (g) threads (h) hydrostatic strength (i) tensile strength (j) air pressure test (k) sampling (l) coatings (m) dimensions.