The IOS S-system drag unit custom parts allow for hooking, while maintaining the drag characteristics of the smooth Shimano reel. Aluminum one-piece machine cut housing delivers precision spool rotation, and the concept of receiving the spool with precision bearings instead of the unstable resin color of the surface pressure of the drag felt is always consistent, increasing the stability of the drag operation, and strengthening the drag characteristics and minimizing the drag output as needed by the linear according to the tension. It evolves into a power game with fish around structures that were not only smooth but long casts, and a wide axis hook. The drags tone is also refined, and the pitch is finely cut to the exact amount of drag performance without compromising the drag. It also comes with a fine tune and an adjustable shim to prevent unevenness of the spool. The Ssystem cannot be reverted. As it is used in conjunction with Shimanos traditional rigit support system, it is not designed to be reversed, so please note that excessive reverse will cause the wear of the system itself. Please be sure to attach the item that fits the reel when purchasing. If not in size, it does not perform or it is worse, you may not be able to wear it. Thank you for your understanding.