I haven't carried one for several years. I've had two broken chains and both were worn beyond the point where they should have been replaced. So, I just keep my chains well maintained and replace them when they should be.
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A conclusion is the place where you got tired of thinking. - S. Wright
Favorite rides in the stable: Indy Fab CJ Ti - Colnago MXL - S-Works Roubaix - Habanero Team Issue - Jamis Eclipse carbon/831