These are rollers with a dual-sprocket at the end. They are used in chain-driven roller conveyors, whereby a single roller is driven from an electric motor via a chain. This roller is then connected to its neighbouring roller by a short loop of chain, and its neighbour to IT'S neighbour, and so on down the length of the conveyor in a 'daisy chain'. (see pictures).
Usually the motor is placed in the middle of the conveyor, to distribute torque more evenly down the daisy-chain of rollers.
The rollers themselves consist of a standard roller, with a double sprocket welded onto it - usually at the very end. This configuration is reffered to as "double simplex". The roller still freely rotates around its spindle (with an internal bearing), differentitating it from a Drive Drum (which is fixed on its axle).
CCBA can provide a range of sprocketed rollers, featuring different roller sizes, and different sprocket types to match your chains.