The double ring system is the most secure of all locking systems hull. As such, this system is the most common in high-end helmets, especially sports, besides being the only approved for use in circuit. But it will not help if we buckled well.
As you can see, the system consists of two metal rings linked to one of the tapes.
To fasten our correctly, we started another tape and go through the two rings.
We can use the red strip to tighten the belt.
We run the entire tape until it clicks and then we had the same tape by one of the rings and re-tighten.
To impede having the belt hanging, this system almost always has a push button.
You can find helmets with double buckle from the best brands in our large section of helmets, and if you filter them by "double buckle fastener" you can make you in seconds with one of them.