3.5mm Mono Jack Plug to 2 x RCA Female Adapter
RCA Audio Splitter Adapter split 3.5mm Male to 2 RCA Female (Mono).
This adapter is commonly used to convert the 3.5mm mono audio from a PC sound card to 2 x RCA female connectors to connect to an amplifier with RCA inputs. See picture for more information.
It can also be used with any other RCA Mono output on a device such as an Xbox 360 to passthrough the audio through the PC Sound card (via Line-In) to the PC Speakers or an amplifier / receiver which has RCA inputs. See attached picture for information.