Kettler Tandem Insert for Kettler Tricycles, Blue & Red Turn a Kettler tricycle into a stretch trike (up to 4 riders) with this tandem insert that has a blue seat with a red frame. This accessory can also be used as a modular tandem insert for Kettler S-frame tricycles. Quickly and easily install on a Kettler tricycle by using the Quick-Adjust knob for secure assembly. Get the maximum comfort ride with high-impact resin bucket seat and handlebars and footrests, along with a 3-year warranty.