Optical fault finders are used to test single-mode and multi-mode glass fibers and other fiber optic components for breaks or faults or to find the right pairs in a bundle of glass fibers. The red light source for fiber optics is equipped with two adapters that can be used to contact almost all fiber optic connectors. 1 x universal adapter for 2.5 mm ferrules (DIN, E2000, FC, SC, ST, etc.) and 1 x adapter for 1.25 mm ferrules for SFF connectors (LC). The wavelength used of approx. 650 nm is very clearly visible. With an optical output power of approx. 1 mW, the red light source corresponds to laser class 2 (IEC 825-2) and can be operated freely without protective measures. Thanks to its small, compact and handy design, the device is ideal for daily use in a wide variety of cabling tasks, both in the open field, in harsh industrial environments and in the laboratory.