This unit carries a roller chain along its outer profile while running on an internal bearing arrangement, keeping tension or guiding the chain path without driving it. The sprocket body is made from steel or sintered iron, mounted on a 25.0 mm bore with an outside diameter of 52.0 mm. Net mass is 0.58 kg. Symbol KSR25-L0-20-10-09-16 identifies the specific bore, width and sprocket configuration within the KSR..-L0 series. The compact bore-to-outside-diameter ratio suits installations with limited radial space where the chain needs a fixed return or tensioning point. As an idler unit it does not transmit drive torque, so loading is limited to chain tension and guidance forces rather than power transfer. Fitment should follow the bore diameter and mounting geometry given by the catalogue symbol, with no substitute reference available for cross-checking against other manufacturers.