The spine of a carabiner contains important information on how much load it can safely bear. The weight that a carabiner can bear varies depending on where the load rests on the carabiner and so there are three different load ratings on each carabiner spine, all listed in kilo Newtons (kN). One kilonewton corresponds approximately to a weight of 100 kilograms.

1. The first rating is for Major Axis Loading, i.e. loading in the longitudinal direction – this is the use for which the carabiner can bear the most weight, i.e. a load pulling along the spine from both ends.
2. The second rating is for Cross Loading, i.e. loading in the transverse direction  – carabiners are not designed to be loaded this way (due to the pressure it puts on the hinge pin at the base of the gate) and so the cross loading rating is always significantly lower than the major axis loading rating.
3. The third rating is for Open Gate Loading i.e. loading in the longitudinal direction with the gate open – this is the load rating of the gate when it is opened while under load. Once again, this is going to be significantly less than the major axis load rating.