With this Oil Gauge / Fuel Gauge you can see the level of the liquid in an oil tank or gas tank. The included ring has an outer diameter of 50mm and is 8mm high and made from well weldable steel. This ring must be welded into the tank. Then screw the brass ring (approx 38mm round)with the sight glass, in the welded ring. The brass ring has a seal so that no leakage occurs.