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CMI Rope Jack

Front View: Closed Rear View: Closed
Front View: Closed Rear View: Closed
Front View: Open for Rigging Rear View: Open for Rigging
Front View: Open for Rigging Rear View: Open for Rigging

Technical Details

I acquired my CMI Rope Jack from Rock'N'Rescue in 2017.

My CMI Rope Jack is 705 mm. long, 80 mm. wide, 44 mm. high, and weighs 972 g. It consists of two ascenders mounted on a milled handle. Each ascender shell is milled from an aluminum alloy extrusion and then painted red. The extrusion direction is oriented parallel to the vertical axis of the ascender, and contains two opposing channels. One channel is rounded and becomes the rope channel, the other is square and holds the cam. The rope channel is 18 mm. wide. Both ascenders are attached to the handle with 5/16" (7.9 mm) bolts threaded to the handle. The distal ascender is attached through a hole above the cam, and has the appearance of having a reduced but traditional ascender handle. The other ascender is less standard, having an extended arm below the cam channel with three lightening holes and an attachment to the handle at the base. Both ascenders can rotate on the handle.

The cams and safeties are the same as those on the CMI Foot Ascenders. The cams are skeletonized, reinforced stainless steel castings. They are spring-loaded and have a (4.3)^5(4) tooth pattern. The cam radius increases from 43 to 62 mm. over a 46° arc, giving an effective cam angle of 24°. A spring-loaded safety on the base of each cam blocks cam opening unless swung out of the way. When the cam is open, the safety may be released to catch the shell, holding the cam open.

The handle is milled from aluminum alloy and painted. It has several lightening holes near the grip end.

Each side of the handle is labeled "Cmi ROPE JACK."


The CMI Rope Jack is an arborist tool designed for tensioning static lines. It can also be rigged for light lifting.

The Rope Jack can easily be misused, causing rope damage. CMI provides the following information that the user should adhere to at all times:

The length of the handle on the Rope Jack limits excessive loading to avoid rope damage. Under no circumstances should a cheater bar be used to increase leverage as it may damage the unit, the rope, or severely injure personnel. It is designed to be used by only one individual using one hand only; and shall be removed before any 'shock' load is applied; it shall NOT be used for heavy or dynamic loads as there are other tools available for those applications…. Cams, even 'untoothed' like a Rescucender and Gibbs, have been shown to shred a rope with high loading. There are much better tools for the heavy work.

Nick Hatch sent me some additional information:

The earliest mention I see of the device is in a forum in 2012, where Jack Holdway discusses development of the device [1]. He worked with CMI to bring a commercial version of the device to market [2]. I've included CMI's description of the tool from the manual [3] below.