This sprocket is 48 teeth 10mm pitch. Note the bearing in the centre. You can also clearly see in pictures three and four, the electro-magnetic clutch plate. When the clutch is engaged, this sprocket transmits drive to the propeller shaft. When the clutch is not magnetised, the assembly simply free wheels which protects the electric motor from being driven to destruction by the main engines. The reciprocal sprocket on the propeller shaft is also 48 teeth.