Unified threads per ASME B1.1 formulas, with tolerances rounded to four places before they are applied, as the
standard's worked examples do. External minor diameter: neither ASME B1.1 nor ISO 965 specifies a minimum
for an external thread — B1.1 para 5.4 says it is "established by the crest of an unworn tool." B1.1 tabulates only
the UNR maximum, as a reference dimension, so that is what is shown; the UN flat-root maximum and the optional
design minimum of B1.1 para 8.3.1(f) are labelled as such. For metric, ISO tolerances only four diameters and does
not include d3, so the value shown is the informative H/6 stress-area reference from ISO 965-3 / 965-4 Annex A, and
the specified root requirement is the minimum root radius. V-shape details are reference geometry. Metric fundamental deviations
use the tabulated ISO 965-1 Table 1 values directly (they are not computable from the standard's formulas);
tolerance grades follow the ISO 965-1 formulas with preferred-number rounding, where a printed table value can
occasionally differ by one rounding step. Nonstandard pitches are refused rather than approximated. NPT per
ASME B1.20.1. ACME and STI are reference geometry in this version. Always verify critical dimensions against the
governing standard, customer spec, or gauge certificates.
Further reading: Measuring Threads with Wires, Start to Finish.