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:, (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