August bicycles was selling a widget to do this with Thompson seat clamps
https://www.augustbicycles.cc/online-store/Light-bracket-barrel-nut-to-suit-Thomson-Seatclamp-and-Supernova-E3-tail-lamp-p245693406
They look neat. I don't have one of those barrel type clamps but I wonder if I could extend a normal seat clamp bolt and add a nut to achieve the same thing?
I just use the elastic band the light came with.
@hippy started
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August bicycles was selling a widget to do this with Thompson seat clamps
https://www.augustbicycles.cc/online-store/Light-bracket-barrel-nut-to-suit-Thomson-Seatclamp-and-Supernova-E3-tail-lamp-p245693406