These jet needles fit Bing 54 carburetors commonly used on Rotax 2-stroke engines. The jet needle works in the needle jet to affect fuel flow to the engine the most at part throttle. The closer the throttle is to full or close, the less influence the jet needle has on fuel flow. Jet needles can sometime where in the clip groves and should be inspected periodically. If wear is detected, replace the needle.