on manually controlled lathes, the thread pitches that can be cut are, in some ways, determined by the pitch of the lead-screw: a lathe with a metric lead-screw will readily cut metric threads (including ba), while one with an imperial lead-screw will readily cut imperial-unit-based threads such as bsw or uts (unf, unc). this limitation is not insurmountable, because a 127-tooth gear, called a transposing gear, is used to translate between metric and inch thread pitches. however, this is optional equipment that many lathe owners do not own. it is also a larger change-wheel than the others, and on some lathes may be larger than the change-wheel mounting banjo is capable of mounting.