Reducing piece with intumescent fire protection fabric for symmetrical reduction in straight duct sections from PLM D 0810 to PLM D 0410. Suitable for direct wall and ceiling mounting, mounting underneath system floors and on support systems. Tool-free joint mounting with PLM SI joint connector. The cover is snapped on without tools and enables quick inspection and subsequent installation. Cover overhang enables offset cover mounting for continuous potential equalization of the entire duct section.