Carabiners
Carabiners are metal loops with spring-loaded gates (openings), used as connectors. Once made primarily from steel, almost all carabiners for recreational climbing are made from a light weight aluminum alloy. Steel carabiners are much heavier, but harder wearing, and therefore are often used by instructors when working with groups.
Carabiners exist in various forms; the shape of the carabiner and the type of gate varies according to the use for which it is intended. There are two major varieties: locking and non-locking carabiners. Locking carabiners offer a method of preventing the gate from opening when in use. Locking carabiners are used for important connections, such as at the anchor point or a belay device. There are several different types of locking carabiners, including a twist-lock and a thread-lock. Non-locking carabiners are commonly found as a component of quickdraws.
Carabiners are made with many different types of gates including wire-gate, bent-gate, and straight-gate. The different gates have different strengths and uses. Most locking carabiners utilize a straight-gate. Bent-gate and wire-gate carabiners are usually found on the rope-end of quickdraws, as they facilitate easier rope clipping than straight-gate carabiners.
Carabiners are also known by many slang names including biner (pronounced beaner).
Read more about this topic: Rock-climbing Equipment