Grado Labs 6.3mm to 3.5mm adapter.

The mini adaptor cable has a 1/8 inch (3.5mm) 'mini-jack' plug with a cable connected to a 1/4 inch (6.3mm) jack plug. The cable eliminates added leverage on the output circuit board of the source.
The mini adaptor cable is constructed of the same high quality wire as their headphone cable. Grado guarantees no degradation of sonic quality with Grado headphones while using their mini adaptor cable.
Converts a 1/4 inch (6.3mm) plug to 1/8 inch (3.5mm) plug.

You can choose in the menu above between a 4 conductor or 12 conductor adapter, the latter being of the highest quality.