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A distancer to fit the length of 3.75mm cutters for milling machines in order to use a suction.
The lenght of the cutter must be 19mm to fit the suction tool, so the inner hole of the tool is about 19mm deep.
Place the cutter into the router, push it down with this tool an then fasten the cutter. Now it has an length of 19mm and fits perfect into the suction of the milling machine.