There are three characteristic diameters (⌀) of threads: "major diameter", "minor diameter", and "pitch diameter": Industry standards specify minimum (min.) and maximum (max.) limits for each of these, for all recognized thread sizes. The minimum limits for "external" (or "bolt", in ISO terminology), and the maximum limits for "internal" ("nut"), thread sizes are there to ensure that threads do not strip at the tensile strength limits for the parent material. The minimum limits for internal, and maximum limits for external, threads are there to ensure that the threads fit together.