This easy to fit tank sender probe only requires one 22 mm (7/8″) hole in the side of the tank and suits tanks from 100 mm to 280 mm (4″ to 11″) deep. The sender probe is sealed by a special grommet which is compressed in the hole when the nut is tightened and measures the water level by contact with the 5 sensors along the arm. It has no moving parts.