Black Diamond
The Fin (bright)

The Fin was Black Diamond's first hot-forged carabiner, very light and large. Most climbers found it too large for practical use, except when ice climbing with mittened hands. It incorporates a finger stop on the spine of the carabiner. The patent describes this feature as:

The spine includes a fin or rib extending rearwardly therefrom, with the fin having a contact surface against which a person's thumb may rest when gripping the spine from the rear. This allows the person to orient, by feel, the carabiner for subsequent use.

Although heavier than many modern carabiner, the large size causes The Fin to feel light in the hand - but oddly balanced due to the light body paired with a large, solid gate. The gate spring tension seems light to me, although the carabiner feels like it would clip rope easily when hung on the end of a quickdraw.

The example pictured here is a factory first, but I also have a factory second. In comparison with this factory second, the flash left from hotforging on the factory first example has been removed more thoroughly, uses domed rivets on the gate and has a stamped batch marking on the spine exterior. See also: The Fin (black)

The 1995 issue of Accidents in North American Mountaineering reported that this model of carabiner hooked the back of a climber's knee, impaling(!) him during a lead fall.