Angular Velocity as a Vector
We assumed that the angular momentum  was a vector pointing along the axis of the wheel as shown in Figure (1a). We can obtain this vector concept of angular momentum by first defining a vector angular velocity as shown in Figure (1b).
We will say that if a wheel is rotating with an angular velocity ω_rad/sec , the vector has a magnitude of ω_rad/sec , and points along the axis of rotation as shown in Figure (1b). Since the axis has two directions, we use a right hand convention to select among them. Curl the fingers of your right hand in the direction of the direction of the rotation, and the thumb of your right hand will point in the direction of the vector .

Figure 1.