This device can be used on ropes up to 13 mm (1/2"). It is simple in design and extremely strong. It is designed for heavier loads (2 person). It has been tested with a 200 kg load that was dropped 1 meter on 1/2" rope from 3 different manufacturers. Each time the fall was arrested causing no visible damage to the ropes and no damage to the Noworries. For complete information and test results from SRTE.