For anyone interested, I am able to confirm that the Shop-Vac 9067900 Right-Angle Round Brush (~US$7) can be used as a 90-degree elbow between Festool dust extractors (and all other dust extractors that utilize a 58mm ID inlet like Starmix and rebranded-Starmix extractors like Metabo, Hitachi, CS Unitec, etc.) and Festool hoses (and other brands of hoses that are fitted with or can be fitted with a friction-fit 57mm (2-1/4") vac-end fitting). To put this in writing: the bristle assembly is easily removed from the "Round Brush" (the two parts simply pull apart) which leaves an elbow, the smaller-diameter-(female)-end of which fits into your vac inlet and the larger-diameter-(male)-end of which accepts the (female) vac-end fitting on your hose, as shown below:
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The elbow is smooth inside (no obstructions) but is not anti-static.
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The elbow is smooth inside (no obstructions) but is not anti-static.