Abstract: A drive system monitors the rotary motion of a shaft and transmits the rotary motion to an encoder. The drive system includes a drive sprocket that is coupled to the rotating shaft by a pair of disc-shaped hubs with the sprocket being sandwiched between the two hubs. The sprocket has an axial bore formed therethrough and is split into semi-circular halves to facilitate circumferential mounting of the sprocket on the shaft to be monitored. The two disc-shaped hubs which couple the sprocket to the shaft have axial bores formed therethrough and are split into two segments each of which is preferably less than semi-circular to allow the hubs to be clamped in circumferential engagement on shafts of various diameters within a predetermined range of diameters. A chain is connected to the drive sprocket for transmitting the monitored rotary motion of the shaft to the driven sprocket of the encoder.