This dust shoe fits an 80mm (3.15 inch) diameter spindle and a 4-inch vacuum hose. On a CNC router table, a dust shoe is used to connect the vacuum hose near the spindle to collect most of the dust and chips during cutting. Set up your router job without the bottom of the shoe attached. Start the dust collector and then position the bottom in place. The suction from the vacuum holds the bottom part of the shoe firmly in place.