The difference is how your door aligns with the side or gable of your cabinet. FULL overlay means when door is in the closed position and you are standing in front of the cabinet you cannot see any of the side or gable. The HALF overlay means that when the door is in the closed position and you are standing in front of it you can see 1/2 of the side or gable. The hinges look exaclty the size however it is the geometry associated with the hinge construction that allows it to be FULL or HALF.

To use this hinge properly on a typical cabinet door you need to bore out a 35mm hole, 7/16" or 11mm deep in the door and there should be 2 hinges/door. The BP or 1 pair pack of this hinge also available on-line and in stores has the necessary installation instructions included. If you purchase this hinge in the AP or 10 pack bag you will also need to purchase the corresponding mounting plate to be able to mount the hinges.