3.5mm KEYSTONE INSERT joins two cables with 3.5mm TRS plugs; Connect cables for a headphone, microphone, IR repeater, MP3 player and more; Fits a standard opening in a wall plate for keystone jacks 3.5mm AUX COUPLER with female ports on both sides connects to a 3.5mm cable concealed behind the wall STURDY SNAP-IN CONSTRUCTION of 3.5mm feed-through keystone provides a secure connection; Re-usable keystone jack inserts can be easily disconnected and relocated when upgrading or redecorating