DDM premium 9500 super high stall high-RPM clutch spring for Zenoah and Chung Yang engines with 54mm clutch. Designed for RC use. This upgraded spring, custom-made of top-quality materials in the USA, offers unparalleled reliability and performance. Stock spring engages at approx 6000 RPM; this spring is 40% stiffer for clutch engagement around 9500 RPM. The clutch will begin to touch at around 8500 rpm, with full engagement around 9500 rpm. Improve your off-the-line power with a higher engagement RPM!