Most modern devices today feature a 4 pin TRRS (Tip Ring Ring Sleave) connector that hosts the two stereo headphone connections, a microphone connection and the ground.
In case you need to connect your headset to a device that has the headphone and the microphone connectors separated you will need this adapter.
This adapter is a 3.5mm TRRS male to 3.5mm stereo and 3.5mm mono female connectors so it can be used on the headphone output directly.
The adapter does not come as a part of the NC-1 headset and is sold separately.