Carabiners

Carabiners are widely used in rope-intensive activities such as climbing, ziplining, caving, sailing, rope rescue, construction, industrial rope work,window cleaning, and acrobatics. They are predominantly made from both steel and aluminium. Those used in sports tend to be of a lighter weight than those used in commercial applications and rope rescue. Often referred to as carabiner-style, carabiner key rings and other light-use clips of similar style and design have also become popular. Most are stamped with a "Not For Climbing" or similar warning due to a common lack of load-testing and safety standards in manufacturing. While from an etymological perspective any metal attaching link with a spring gate is technically a carabiner, the strict usage among the climbing community specifically refers only to those devices manufactured and tested for load-bearing in safety-critical systems like rock and mountain climbing.

Source: Wikipedia