Built this throttle because my little one had a hard time holding the Razor Scooter's throttle on for extended time, before their hand began hurting. I printed both tubes separately standing vertically with openings pointing down and without support on the Prusa i3 using 1,75mm PLA.
First remove the black handle on the scooter, then loosen the allen lock screw on the throttle. Install the plastic inner bushing and re-tighten the throttle in place so that the bushing is fully on the handle bar shaft. Then install the larger throttle tube, taking care to use a flat blade screwdriver to force the rubber throttle inside. No glue is required as this is built as a friction fit and easily undone.