This adapter is designed to be connected between a track (or monopoint or an extension arm) and a track head. It provides an extended range of positioning for the track head, which is very useful for certain applications.
For example, if you mount your track on a sloped ceiling, this adapter lets you point the track head exactly where you need it.
Also, you can illuminate artwork or displays by mounting track to a wall, then inserting an extension arm. Then add this knuckle adapter and a track head. The knuckle adapter allows you to point the light back at your artwork or display.