CMI RNA Pulley

The CMI RNA pulley is a small, light micro pulley built for rope access style systems, and tree climbers use it as a hitch tender and in small mechanical advantage setups. It clips onto a carabiner below your friction hitch and keeps slack moving through as you climb.

How climbers use a micro pulley

On a moving rope system the most common job for a micro pulley is tending the hitch. The pulley rides on the bridge carabiner below a Distel or VT, and as you pull slack up through the system the sheave pushes the hitch up the rope. It saves you reaching down to advance the knot on every pull and makes footlocking or body-thrusting smoother.

The same pulley earns its keep off the saddle too: a small redirect, a pulley on a tag line, or the moving pulley in a light-duty haul. See our other micro pulleys to compare size and weight.

Fit, inspection, and care

Check the side-plate marking for the rope diameter range and rated strength, and make sure your hitch cord and climbing line fall inside it. A rope that is too big for the sheave rubs the side plates and loses efficiency.

Before each climb, spin the sheave and listen for grinding, look for grooves worn into the sheave or plates, and check that the side plates close fully on the axle. Keep it clean of sap and grit. Any pulley in your life-support system has to be inspected before use, and life-support use must follow ANSI Z133, the manufacturer's instructions, and your training.