What Is The Dia Of The Gear Stick?

[Atari Boy 11]

As above, does anyone know the diameter of a 1989 GTi, knob end (forgive the pun)?

[HERMAN 33]

I have had a nylon one turned up for mine I drilled it out to 11m and that was to small 11.5 mm was also to tight so I tapped the knob out to m12 and then screwed it over the barbs on the top of lever. Seems fine but I can turn it if I want to.