In 4 synchro gearbox it's a critical part of the close ratio gear set. Be sure to check your old one for wear on the inner surface of the layshaft bearings; it wears out far faster than the gear teeth! Pre A+.Original ST Abingdon profile and design ratiosBeware the Clubman laygear has the same gear counts but has an identification cut mark on the 3rd gear of the laygeari.