Center distance (mm) 25 30 40 50 63 75 90 110 130 Ratio 7.5 10 15 20 25 30 40 50 60 80 100 1.Made of high-quality aluminium alloy, light in weight and non-rusting. 2.Large in output torque. 3.Smooth in running and low in noise. 4.High in radiating efficiency. 5.Good-looking in appearance, durable inservice life and small in volume. 6.Suitable for omnibearing installation.