This is a 7 to 4 trailer wiring connector adapter.  This will adapter will work if you have the 7RV (6 spade connectors around 1 center pin-- common on most new trucks and SUV's) on your tow vehicle and the 4 flat (3 female holes and 1 male pin) connector on your trailer.  This plastic adapter has handles to help with inserting and removing the adapter.  It also has a stop that engages with the flapper door on your vehicles connector to make sure it does not come out while towing.  This adapter will run your brake lights, running lights, right turn signal, and left turn signal.