2.5mm Stereo Plug to 3.5mm Mono Jack Adapter. 2.5mm Stereo Plug to 3.5mm Mono Jack converts 3.5mm Mono Plug to a 2.5mm Stereo Plug. The adapter is assambled of black molded plastic with nickel-plated contacts. Black molded plastic construction. Nickel-plated contacts. Connector 1: 2.5mm Stereo Plug. Connector 2: 3.5mm Mono Jack. External Length / Height: 37mm. Body Diameter: 10mm.