How to fit a Storage Options bike cam helmet mount
It's designed so the bit at the top of the picture wraps around the helmet like a headband while the part of the strap that is making a "U" in the picture goes across the top.

To keep it from coming off, you'll need it to be fairly tight. This is okay with the helmets that are similar to skateboarding/snowboarding helmets (hard shell), but can make some of the more pricey (lighter) bike helmets lose integrity.

If you aren't going hard down single track, this will probably be okay, but be ready for it to slip off if you are doing anything that rocks the boat much.