Rubber thing. It is worn on top of the drill and is fixed with a rubber washer (in the set of 2 pieces of these). Drilled two trial holes in white brick. Well, in general, I managed my work. 95% dust left inside. The only thing that is uncomfortable is to bend the rubber to aim and there is no constant visual control of the depth of drilling. It is necessary to stop periodically, to bend the rubber and watch the drill enter the wall deeply. In general, the thing is good in the economy.