The knob and lower ring are both screwed onto a threaded cylinder which is held onto the gearstick with three tiny allen grub screws, which often work loose. It is sometimes be difficult to unscrew the lower ring, so wrap it in a bit of rubber strip and grip with a mole wrench or gas pliers to get it going, whilst holding onto the knob.
An identical gear knob can be obtained direct from “Richbrook”, usually much cheaper than other suppliers.
