Clutch Masters 850 Race Twin Disc Clutch Kit | 2004-2019 Subaru STI (15017-TD8R-SW)04 19 STI 850 Race Twin Disc Clutch Kit by Clutch Masters The 850 series is a larger diameter assembly, which is designed for high horsepower applications. The 850 Series has a higher holding capacity, less clutch chatter, and a smoother engagement compared to the 725 Series. The 850 series Twin disc will accept one sprung disc creating a slightly smoother engagement compared to two rigid discs Clutch Masters Twin Disc systems are pure racing