These plastic bushes are designed to slip on the steering rack to limit the amount of lock available.
These are typically used on lowered cars to stop brake calipers from touching on the tie bar and on cars fitted with 13" wheels to stop the wheel from touching bodywork.
Two sizes are supplied in the kit to cover the types of racks used in production Minis. The older style racks have a screw together joint which is threaded over the end of the rack. These use a split collar style rack stop spacer. This fits over the rack without dismantling whereas the latest racks have a sealed drumstick which screws into the end of the rack and these use a solid spacer which requires the drumstick to be unscrewed in order to fit.
Split collar dimensions 36.6 OD x 27.25 ID x 12mm wide
Solid spacer dimensions 37 OD x 22 ID x 12mm wide