This light replaces the standard Caterham rear NP light, which always lets water in and rusts (because it is fitted upside down :) ) It is cheaper than the one at £16 because it has 4 leds instead of 6 but 4 leds is really quite bright and far brighter than the standard Caterham light which has two bulbs. The bolts supplied are far too long but can't be cut to size because the first 20cm of the bolts have no thread. So you will need a couple of new bolts or use the ones from the existing light.
Blue7