Wilwood's Master Cylinder Reservoir Caps with Electronic Fluid Level Sensors: Checks fluid level electronically and indicates when fluid level needs attention. Utilizes standard automotive 12V DC male terminals for long service life and easy installation of the electrical circuit. Caps are manufactured from durable lightweight Nylon which has a high melting point and superior color fastness, perfect for engine compartment environments. 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.