They are usually D-shaped or oblong metal ring, with one spring-hinged side. It is used primarily in mountain climbing, as a connector and to hold a freely running rope.
The word comes from the German word “Karabinerhaken”, which means “hook for a carbine”.
A carabiner or karabiner is a specialized type of shackle, a metal loop with a spring-loaded gate. Carabiners are used to quickly and reversibly connect components, most notably in safety-critical systems.
D-shaped carabiners are considered to be the strongest and most durable on the market. They have a smaller gate opening than other shapes, but they still have a larger gate than oval carabiners. They are reasonably affordable and excellent for a wide range of climbing exercises.
Freskaro carabiners use 7075 aluminum with a very high strength rating compared to other climbing equipment like harnesses and rope, you’ll be safe using an aluminum carabiner in almost all applications.
Otto Herzog (1888-1964) was a German climber and inventor; he got his nickname “Rambo” 70 years before the “Silvester Stallone’s” movie franchise of the same name :-)