The Fuel Rail for the new style throttle bodies is the 2nd purchase you make, right after the exhaust End Cap. It gets Fuel to the injector with no hesitation, everytime you crack the throttle. You can see how the stock Fuel Rail ( Black plastic ), shoots the incoming Fuel down and away from the injector, causing interuptions and hesitations in throttle responnse. Ours ( aluminum ) shoots the Fuel stream directy into the injectors pick up hole. Throttle response and get up and go are improved dramitically. Changes in minutes with throttle body still on bike. Fits all 2017-2021  250-501 ktm's and husqvarnas