Right now I've just got a PB superflash and I had a radbot 1000 on there, but I have the rear light that goes with the magicshine set. If you were to move to something like the magicshine system (rather pricey), I'd imagine the o-ring attachment system would allow you to use just about any shape of seat tube. Don't know though.
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Bikes: 1996 Eddy Merckx Titanium EX, 1989/90 Colnago Super(issimo?) Piu(?), 1990 Concorde Aquila(hit by car while riding), others in build queue "when I get the time"