Fiber optic Adapters and Fiber Optic Fast Connectors are designed to connect two fiber optic cables. They come in versions to connect single fibers (simplex), two fibers together (duplex), or sometimes four fibers together (quad). Fiber optic connector adapters are designed for multimode or single-mode cables. Fiber optic cable adapters have FC, SC, ST, LC, MT-RJ, MU, simplex, E2000, FC/APC, duplex, SC/APC, LC/APC, E2000/APC, quad, mating sleeves, hybrid fiber optic adapters, single-mode fiber optic adapters, multimode fiber optic adapters.