Genuine Mini Spares product as everything else on the market was poor fitting and unstable.
For Performance see
88G459EVO made in the USA by a Specialised Racing product company.
All the earlier heads used the 2A11 cotters, noted by the wide slot in the valve. All pre 1984 12G940 castings and Cooper S used these collets
Later 998/1098 production from 1970 on and most aftermarket valves, use this
88G459 collet/keeper with a single narrow groove Pre A Plus.
Valve stems with 3 grooves as used on most A-Plus heads late 1980s on,use
CAM6975 cotters. Order the correct cotters to go with the valves you will be using.
When ordering these you get two halves to equal one cotter for one valve.