1PORTABLE DESIGN: Visual fault tester, portable design, light and practical, easy to operate and carry, is a common tool for optical fiber testing. 2MAIN PURPOSE: Specially designed for maintaining optical cables and lines, used to locate cables and detect whether optical cables are defective. 3CONTACTLESS CONNECTION: The end faces of optical fiber and transmitter are not damaged, and the output power is not affected by voltage fluctuation. 4WORKING RANGE: The output wavelength of the red light test pen is 650nm 10nm, with stable output power and wide application range. 5ALUMINUM ALLOY: The pen shell is made of aluminum alloy, which is corrosion and abrasion resistant, and can be used in various environments.