Aumo-mate Car/auto/vehicle Handle Control Steering Wheel Knob Clamp Steering Wheel Spinner, Power Aid Balls (Carbon Fiber Black) Diameter of mounting hole: Approx. 1.18-1.37 inches / 3-3.5 cm, fit for steering wheel thickness below 1.37 inch / 3.5 cm. When turning car, it lessens the turning radius and helps beginners and lady drivers to drive safely and conveniently. Make the steering wheel no longer heavy, more relaxed for driving. Adjustable spinner knob, turns freely when the connection to the wheel needs to be tight. The knob is made of ABS plastic and the base is made of stainless steel.