There were two types of the early gear knobs.
The very early (first) type had the thread cut straight into the "bakelite" and were locked on to the lever with a thin hexagonal nut.
The more common second type had the thread cut (as it was first screwed on) into a rubber insert and no lock nut. The theory was it helped damper vibration.
Fully imported built up early Coopers had the first type.

Thanks for all the feedback. Are replicas still about for sale?

May try to make one myself and look laser cut options in the market. The challenge will be thr chamfer on thr top insert around the edge i think.

Can anyone tell me are thr blue/white checkers a plastic or gloss paper or card, and is it on the base of the bottom insert?

Now here's some information you won't find on Google, but you will find on Page 135 of the Mini Clubman Engineering nDrawings book (which no doubt all fastidious owners have). The proportions of the badge are given there, but it is intersting to know that the letters GT are engraved in the upper insert and are coloured bright red (including the vertical sides of the engraving) while the 1" dia blue check pattern 0.12" dim (described as "blue hot stamped") appears as a separate flat insert underneath. Regards, Tony