The 850 series is a larger diameter twin disc clutch 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 Twin Disc. 8.50 in. (Race/Street). Bearing included. Flywheel sold separately Must use CM Flywheel: FW-S8-B-TDA