These shrouds fit Bosch angle grinders to form a barrier that keeps silica dust contained so it can be sucked into a dust extractor. They have a port to connect a hose from the shroud to the extractor. Shrouds are used as part of a dust extraction system to comply with OSHA’s Respirable Crystalline Silica Standard, which governs exposure to silica dust from cutting, drilling, grinding, or surfacing stone, concrete, brick, and mortar.