Anyone have any bright ideas on how to re-fix the gas control knob on
a Camping Gaz luminare?

The knob is plastic the shaft splined brass (no split). The plastic
is too soft or splines not big enough to take the torque so the knob
is now more or less round inside. I've tried araldite which worked
until SWMBO'd turned it off too hard... Investigation shows that the
araldite has stuck to the brass OK but failed with the plastic knob.

The shaft is only about 4mm dia, and fully recessed into a housing.
The small dia would make cross drilling it for a pin will be tricky.
The knob is very soft plastic so a simple grub screw onto a flat
filed onto the shaft probably won't work either.

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Cheers
Dave.