The hub dynamo has two identical flanges. For connection of the spokes, each flange has 18, 2.6mm holes at a pitch angle of 20°and at a pitch circle diameter of 80 mm. The flange at the side of the electricity cable is called the back flange and the other flange is called the front flange. For use ina bicycle, the back flange side of the dynamo has to be mounted at the right side of the bicycle to realise the correct direction of rotation of the hub. The rotor is connected to the front flange and this means that the rotor must rotate left hand to realise the correct direction of rotation of the hub. The front flange has a collar with a diameter of 64mm. A moon shaped excisionis made in the blade root for centring on the collar.