Faria Beede offers comprehensive line of marine gauge styles to fit your boat or upgrade needs. Faria Euro Black 4" Speedometer 55mph Mechanical Manufacturer Part Number: 32810 Euro Black 4" Speedometer - 55mph 4" Mechanical - Bore Size: 3.375" 85mm Pitot Tube Type Speedometers are pressure operated from water being forced into the pitot tube. This pressure is transmitted through flexible tubing to the moving bourdon tube inside the speedometer head where it is converted into a speed reading by the moving mechanism. Benefits: