DMM American O Carabiner

The DMM American O is a symmetric oval carabiner with an auto-locking gate. The oval shape keeps pulleys, rope grabs, and rings centered, which is why arborists use it where a device needs to sit square.

Why an oval

An oval carabiner has the same curve top and bottom, so whatever you clip into it settles in the middle. That matters for pulleys, rope grabs, and multi-piece setups where a D shape would let the device slide toward the gate side and load unevenly.

Ovals are slightly weaker than a D of the same material because the load sits farther from the spine, but for many arborist jobs the better device alignment is worth it. An auto-locking gate means it closes and locks every time without a second thought.

Inspection and retirement

Before each climb, open the gate and let it snap shut. It should close fully and lock on its own without sticking. Look for cracks, sharp edges, grooves worn by rope, and deformation at the nose or hinge. Sap and grit are the usual cause of a lazy gate, so rinse and dry the carabiner and keep the gate mechanism clean.

Retire any carabiner that has been dropped from height onto a hard surface, shock loaded, or shows wear you cannot explain. Read the markings on the spine and confirm they meet what your system needs. Life-support gear must meet the applicable standard (ANSI Z133 and the manufacturer's instructions), be inspected before every climb, and be used only by trained climbers. See more auto-locking carabiners.