The Zk -2 Singing Tree Rope Wrench (STRW) is manufactured and distributed worldwide by ISC. The STRW enables Single Rope Technique (SRT) climbing, minimises slack in the system, ensures consistent friction, allows 1 : 1 efficiency, allows simple re -directs and can easily be set up on multiple limbs. The Zk -2 model has rounded side plates and pins for minimal rope wear. It is fitted with a pulley wheel, to support the rope radius and minimise rope compression. The ZK2 It is not intended for use as a primary support.