The Singing Tree Rope Wrench ZK-2 (STRW) is one of the most popular tools used by arborists when they work using single rope technique. The STRW adds friction by creating a ‘bend’ in the rope, above the climber’s friction hitch. With the addition of a stiff tether, the STRW created a 'contained double rope system', on a single line of rope. This contained double rope system travels with the climber as they move around the tree, allowing a consistent level of friction on the hitch, which is often impossible to achieve in double rope climbing. The stiff tether is professionally spliced by the experts from At Height. It features a stiff rubber bumper to prevent the STRW from going into 'neutral' and is made of 8mm Beeline cordage wrapped in several layers of adhesive shrink tube. The tether has an overall length of twelve inches. The RP281 pulley from ISC was designed specifically for the Rope Wrench system. It has swivelling side plates and , a bushing wheel, and weighs only 2.7 ounces.