This was designed specifically for the AirFit F20 and the AirTouch F20 and the AirFit F30. It is not designed to be used on any other masks. This strap is designed to add stability to the mask and prevent leaks. The strap attaches to the mask over the hose connection and then wraps around your head and connects with velcro on the side. There are 2 pieces of velcro at one end, you can cut between these to shorten the strap if necessary. There is a black strip covering over a central piece of velcro that you can remove if you want to attach it to your headgear.
You can do a quick test to see if this will strap will help with your particular leak:
It is a bit much to add another strap around your head, but it does work well if that is your main issue. The installation instructions are included in the package.
Do not use on a mask where it may cover the vent holes near the hose connection.