Black powder coated aluminum extension. Adding length to your rack with only 500 extra grams. Do take some sanding, filing and greasing for the best fit. Mounting guide: Use a round or semi round file to take off any grates on the inside of the rack where the two tubes are welded together. Sand down the first 20cm of the rack. Grease it up and test each side of the extension separately to see if they slide in with the desired resistance.