Berson reactors with an automatic wiper sweep the outside of the quartz sleeve on a timed cycle. Scale, iron and organic film attenuate UV-C before it reaches the water, so a wiper that has stalled or is wiping unevenly shows as falling measured intensity on lamps that are still good. This is the type B boss, the fixing that clamps the wiper rings to the wiper rod. Original Berson number 2.21.316. The type B and the 23T2V009 boss are not interchangeable — check which is fitted before ordering.