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This clever bracket clamps to the saddle rails. This arrangement allows you to mount a Moon Comet rear bicycle light in a prominently high position to help ensure it's clearly visible when you night ride. This arrangement is also useful if their isn't sufficient space on the seatpost to fit the original bracket that comes with a Moon Comet rear light.
The bracket's nylon clamps are easy to secure to the saddle rails via a single Allen bolt - you'll need a 3mm Allen key to fit or remove this light bracket making it less likely to get stolen.