Brake oil test pen is based on variation in electrical conductivity to determine the moisture content of brake oil changes Brake fluid tester is suitable for professional use in automotive repair shops to test Red needs brake oil replaced immediately, green said to be in good condition, just yellow said condition but will change brake fluid tester is designed without connector of cable, portable and lightweight, easy to carry and use Through the light-emitting diodes (LED) clearly shows the degree of water content Description: < p>The main function of this brake fluid test pen is determining brake fluid quality. 5 LED display the percentage of water content in brake fluid, provides more test results Accurate. Brake Fluid Tester is suitable for determining the quality of brake fluid and escorting your driving safety. 3-color illumination is intuitive and convenient. Red indicates that brake fluid needs to be replaced immediately. The green color indicates that the brake fluid is in good condition. Yellow indicates brake fluid remains good, but will change. The brake fluid tester determines the change in brake fluid moisture based on changes in conductivity. humidity is clearly indicated by the LEDs. High levels of humidity will lower the boiling point and affect braking performance. Features: Colour: black. Size: 150mm < p>Material: Plastic Package includes: 1 * brake fluid tester. Notes: Due to the setting difference of light and screen, item color may be slightly different from the pictures Please allow slight dimension difference due to different manual measurement.