Most fiber optic connectors are plugs or so-called male connectors with a protruding ferrule that holds the fibers and aligns fibers for mating. They use a mating adapter to mate the two connector ferrules that fits the securing mechanism of the connectors (bayonet, screw-on or snap-in.) The ferrule design is also useful as it can be used to connect directly to active devices like LEDs, VCSELs and detectors.