Transverse Diametrical Pitch of Helical Gear is usually measured using the 1 per Millimeter[mm⁻¹] for Reciprocal Length. 1 per Meter[mm⁻¹], 1 per Kilometer[mm⁻¹], 1 per Mile[mm⁻¹] are the few other units in which Transverse Diametrical Pitch of Helical Gear can be measured.