As you belay another climber, your locking carabiner is always prone to shifting and rotating within your belay system, especially when the rope is not weighted. Apart from being extremely annoying, the danger of carabiner rotation is cross loading.
All carabiners are strongest along their major lengthwise axis. Cross loading a carabiner along its minor axis (gate to spine) can be dangerous, as this direction has less than half the strength of the major axis. If your climber were to fall when the system is cross loaded, the carabiner could potentially fail.
Black Diamond has solved the cross loading problem with the innovatively constructed GridLock Screwgate Carabiner. Designed specifically for belaying, the GridLock isolates your belay loop behind its uniquely shaped gate, continually holding the carabiner in the proper orientation. A strong, I-beam shaped spine transitions into a large, rounded rope bearing surface for maximum strength and smooth rope feeding for either belaying or rappelling.
Black Diamond says you can safely orient the GridLock carabiner with your belay loop either separated into the small portion or larger portion inside the gate. However, I find the whole system works best with your belay loop down in the small portion, away from the screwgate completely.
In order to pass your belay loop in and out of the smaller opening, you need to keep the carabiner gate open with the lip retracted. This movement takes some getting used to, but gets quicker as you become more familiar with using the special carabiner.
I use a Petzl Reverso 3 for my belay device. I like to have the Reverso oriented with the brake side facing out and down for smooth operation. The GridLock enables me to quickly and easily get my whole belay system in the proper orientation every time.
I tested the GridLock on a couple of multi-pitch ice climbs. As usual, the carabiner worked great for belaying the leader but I didn't like using it for rappelling, as the fixed setup tended to twist my PAS for some reason. I was also uncomfortable with the increased opportunity for dropping my belay device, as I had to completely remove my Reverso from the carabiner while leaving the gate open to extract or insert my belay loop.
Bottom Line: The Black Diamond GridLock Screwgate Carabiner adds an important level of belay safety and convenience, perfect for top rope or even single pitch ice and rock climbing.
The Black Diamond GridLock Screwgate Carabiner retails for $20 and is available now.