For both MMF and SMF. Air-gap type, so RL=-14.7dB. You need cables with FC/APC connectors if high return loss is rquired. There is one red plastic dust cap at one side of adapter, and one metal dust cap at the other side of adapter. Fiber cable is not included. These female to female air gap Attenuators insert loss which depends upon axial misalignment of optical fibers. Attenuators are used for variable suppression of optical signal in SM and MM links. Attenuator takes the place of a standard mating adapter between two male optical plugs. The attenuation setting is continuously variable and controlled by turning the control ring while the connected plugs maintain azimuthal orientation one against another.