Types RCK 19 & 20 are normally referred to as Clamping Discs, used to clamp externally onto thin walled hubs to lock them to the shaft. The design permits the use of large diameter shafts with small hub sizes, and is popular for connection of large sprocket and pulleys. The design provides for optimum concentricity, with high torque transmission. A number of shaft diameters can be accommodated by one size of unit, max., min. and an intermediate.