The CMI Rope Jack is a Mechanical Advantage tool for pre-tensioning static lines, light lifting and cabling. The Rope Jack is small enough and light enough to be carried aloft by a climber for Mechanical Advantage within the crown. 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. lt is designed to be used by only one individual using one hand only; lt shall be removed before any'shock' load is applied; lt shall NOT be used for heavy or dynamic loads as there are other tools available for those applications. It can attach mid-line and can run virtually any length of rope. The MA is approximately 5:1 - no pulleys, no extra rope, minimum weight, minimum friction, quick, easy on-off, works well 'topside', too. The CMI Rope Jack is used to remove slack & stretch for lowering and to lift the tips on light limbs without having to break out the big guns. It is NOT for heavy loads. 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. The rope jack is approved for life support use as long as another form of progress capture device is used in conjunction with the device. Never use the Rope Jack by itself for hauling human cargo. The CMI Rope Jack is approved for static ropes from 3/8-5/8" diameters. Testing has shown that a single person can generate somewhere between 300-80O pounds of force while using the Rope Jack. Testing revealed CMI ascenders will strip the sheath of brand new 1/2" rope at roughly 1500lbs). To remove a load from the Rope Jack, pull the handle and allow the trailing cam to loosen, then pull handle again and allow the forward cam to loosen. Releasing the Rope Jack will take a little practice. The Rope Jack should be relieved from tension a little bit at a time off each cam.