Cantilever boss thread ?

[rob f]

Hi I'm currently building up a tandem using a 1952 Claud Butler frame. At some point it has had cantilever bosses installed & I'm trying to work out what the thread is to get some replacement bolts. It's definitely not an M6 like is used today for cantilever brakes. Anyone got any ideas ?

 

[keithglos]

I think Mafac brazed on had the same as the bolt on, 5mm with a large shallow head 12 or 13mm? Could be alternatives. When I brazed on Weinmanns they were 6mm.

 

[rob f]

thanks Keith. I tried an M6, but they're kind of loose until the threads start to cross. I was given some dia compe cantilevers with the frame but no bolts. I'm not sure if they are the original calipers that the bosses were brazed on for. I'm guessing they might have been Mafac.....

 

[keithglos]

If 6mm is loose and wrong thread it is closer to the old 1/4 inch BSF, but I can't remember any British braze on brakes.
Trying to remember, but now I think Mafac were 6mm.

 

[rob f]

Thanks Keith. I'll check that the M6 doesn't fit again, after all the threads in the bosses could probably do with some cleaning up.