The Blocfor DUO can be attached to the structure with 1 hook if you need to pass an obstacle or move to another anchoring point. Then the 2nd hook can be attached to the structure without risk of not being secured. When the second hook is attached, you can remove the first hook. This way you are always secured. The Blocfor DUO can be used for maintenance work in gondolas, on scaffolding, climbing masts and pylons.