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+. For A Plus see
C-22A1737A 15-19-23-25 TEETH COUNT.
Original ST Abingdon profile and design ratios
Beware the Clubman laygear has the same gear counts but has an identification cut mark on the 3rd gear of the laygeari.
See table of "Straight Cut Gear Kits" and their components
Click Here