Size is 2" X 3 1/2" The arm is 3" long. The Guide traffic light viewer works on the prism principal to reflect a clear image of overhead traffic lights. No stooping, squatting or squinting is necessary...a quick glance in the viewer tells whether light is red or green. The plastic prism in chrome plated base mounts on top of the instrument panel directly ahead of driver seat. This part is useful to many drivers even without a Sun Visor on the car.