Gear & Kit
What The Numbers Stamped On A Carabiner Mean
Carabiner markings give tested strengths in three orientations and a gate-open figure, describing laboratory conditions that differ substantially from how gear is loaded in the field.
Every climbing carabiner carries three numbers and a set of small pictograms. They describe a laboratory test, and reading them correctly changes how the piece should be used.
Three axes, three figures
The largest number is the major axis strength, measured with the load pulling lengthwise along the spine with the gate shut. This is the orientation the carabiner is designed for.
The second figure is the minor axis, measuring a load pulling across the carabiner sideways. It is dramatically lower, typically a small fraction of the major axis value.
The third is major axis strength with the gate held open. It is also much lower, because a closed gate contributes structurally rather than merely retaining the rope.
Why the low numbers matter more
Nobody plans to load a carabiner sideways. It happens when the piece rotates against rock, when a sling twists, or when a nose catches on a bolt hanger.
Gates open unintentionally too. Vibration from a rope, contact with the rock, or the stretch and snap of a fall can flick a gate open at exactly the wrong moment.
Most carabiner failures in the field involve one of these two conditions rather than a genuine overload in the intended orientation.
What kilonewtons describe
Strengths are marked in kilonewtons, a unit of force rather than of mass. Force in a climbing system is generated by acceleration and deceleration, not by hanging weight.
This is why the rated figures look enormous compared to body weight. The relevant comparison is peak force in a fall, which climbing ropes are specifically designed to keep low.
Certification also involves a minimum, not a typical value. Individual carabiners generally exceed the marked figure, but nothing about the marking guarantees a particular sample will.
Locking and shape
Locking gates reduce the chance of accidental opening. Screwgates rely on the user closing them, and screwgate collars can vibrate loose over a long day.
Auto-locking designs remove that dependence and add mechanical parts that can jam with grit, ice or corrosion. Neither type prevents cross-loading on its own.
Shape matters for the same reason. Pear-shaped and HMS carabiners are wider at the top for knots and hitches; smaller wiregates save weight on gear placed for a moment.
Retirement is about damage, not the marking
A carabiner that has been dropped a long distance onto rock may carry cracks invisible to the eye, which is why many climbers retire dropped gear rather than assess it.
Rope running over aluminium wears grooves, and a sharp edge inside a worn carabiner damages rope. Fixed lowering carabiners at popular crags are replaced for this reason.
Manufacturers publish inspection and retirement criteria for each product, and those instructions, along with in-person instruction, are what a climber should be working from rather than a general article.
