Carabiners are metal loops (usually aluminium) with sprung or screwed gates that allow rope or other climbing equipment to be quickly inserted or removed. Carabiners can be broadly divided into two categories, non-locking carabiners and locking carabiners. Non-locking carabiners have a sprung gate that wil snap back into place after the climbing equipment has been pushed through it. Different types of gates are available, including straight gates, bent gates (which allow equipment to be clipped in more easily) and light-weight wire gates. Locking carabiners have an additional sleeve around the gate, which will only allow the gate to open when it is correctly positioned.