Wilwood's Master Cylinder Reservoir Caps with ElectronicFluid Level Sensors: Checks fluid level electronically andindicates when fluid level needs attention. Utilizes standard automotive 12V DC male terminals for long service life and easy installation of the electricalcircuit. Caps are manufacturedfrom durable lightweight Nylonwhich has a high melting pointand superior color fastness, perfect for engine compartmentenvironments. The internal float is made from a proprietary material,offering excellent dimensional stability to yield accurate readings. Cap diaphragm provides positive sealing and long service life in brake fluid environments. Direct replacement caps for the most popular size Wilwood brake fluid reservoirs. Part No. 330-12645 fits 4 oz reservoirs.