The switch button and Turbo button are labelled in the red box in the picture, and are captured in the housing from the inside by the inverted triangular end of the structure shown in the picture.

The green box in the picture shows the bottom plastic knob, and the Shell is held together from the inside and can be rotated.

The yellow box in the picture shows the resolver, which is fixed to the Shell with the bottom knob from the inside, while it can work by connecting the circuit board and the motor from the circular structure in the middle.