Pitot tube type speedometers operate by pressure from the water being forced into the pitot tube. This pressure is then transmitted through flexible tubing to the bourdon tube movement inside the speedometer head where it is converted into a speed reading by the movement mechanism. If your marine speedometer is displaying an inaccurate speed or shows no speed at all, the problem is usually with the pitot. Change old or warn pitot assemblies with this universal replacement pitot tube from Faria. Kit comes with 20' tubing.