CMI 5/8" Steel Arborist Block

The CMI 5/8 in steel arborist block is a rigging block for lowering wood on 5/8 in rope. A steel sheave stands up to the heat and wear of repeated heavy lowering, and CMI hardware has a long record in rope rescue and tree work.

Where an arborist block fits

An arborist block is the top of a natural crotch alternative: hung from a sling above the work, it gives the rigging line a smooth, low-friction path. That cuts rope wear and puts the friction where it belongs, at the lowering device on the trunk, so the ground worker can let pieces run and stop them smoothly.

A 5/8 in block suits crews running 5/8 in rigging line for medium to heavy wood.

Steel adds weight compared with aluminum, but for a block that stays rigged in one place through a removal, durability is worth more than a few ounces. Pair it with a sling and lowering device rated to match.

It also suits crews who rig hard every day and want a block that outlasts the rope running through it.

Hanging and inspecting

Hang it on a properly rated sling, girth hitched or choked high enough to clear the piece, with the line running straight through the sheave. Keep the block above the cut so forces stay in line with the stem.

Before every job check that the sheave turns freely, side plates are straight and close properly, and there are no cracks or deformation. Retire a block that has been overloaded. Rigging gear must be kept separate from climbing gear, and crews should be trained to ANSI Z133.