One of my pet peeves is looking down to my belay ‘biner – especially when the leader is hanging on the rope – to see it cross loaded. Spend enough time in the belayer’s shoes and this will happen to you. That is, unless you’re using a ‘biner specifically designed to prevent this from happening.
To clarify, cross-loading happens when a carabiner is stressed horizontally on its minor axis: On one side the rope stresses horizontally against the gate, nose, or locking sleeve and center of the spine. Carabiners are strongest when stressed on their major axises meaning directly in line, vertically, along the spine. When a carabiner is stressed on its minor axis it’s generally one third as strong.
It’s not uncommon for the ‘biner to spin 180 degrees from time to time while belaying a top rope or lead climber. This is why there are specific ‘biners designed to prevent cross-loading from happening.
Carabiners, and especially lockers, are extremely strong and are designed to break under forces that are impossible or nearly impossible to experience while in the field. ‘Biners are built to withstand high levels of force, like when catching the falling climber, whether cross-loaded or not.
Though relatively new to the market, there are a few locking carabiners that are specifically built to prevent cross loading. These are the DMM Belay Master 2 which has been around the longest, the Sterling Falcon AL with Talon, Concept SGL Locker distributed by Liberty Mountain and most recently the Black Diamond Magnetron Gridlock, and Metolius Gatekeeper.
The DMM Belay Master 2 has a bulky plastic shield that folds in place to prevent the biner from cross-loading. The Magnetron Gridlock closes with magnets, making it truly ambidextrous and especially easy to operate with one hand. However, it has a unique body and a L- shaped bar at the base of the gate which makes it time consuming to thread past the belay loop. I have not used the Concept SGL or Gatekeeper.
After months of using the Magnetron Gridlock, I switched to using the simpler-to-use Sterling Falcon AL with Talon, which has a spring tensioned hook to keep the ‘biner properly oriented. This also makes the AL with Talon easier to thread on the lightweight Sterling Chain Reactor or heavier Metolius PAS 22 when belaying off the anchor while above the climber.
It’s been my experience that ‘biners specifically designed to prevent cross loading provide, at the very least, peace of mind. Since these carabiners are specialized, they work work best when belaying directly off your harnesses’ belay loop.