A trolley for lifting and/or moving a load on lines and an installation and method using it are disclosed. The trolley includes first and second side plates and sheave assemblies. Each sheave assembly includes a sheave axle with an axle shaft projecting from the first plate, a sheave cartridge on the axle shaft between the plates. Each sheave cartridge includes a pulley wheel rotatable on a bearing around an axis of the axle shaft. The axes of the shafts are parallel to one another. Retention fasteners extend thought the second plate to secure the second and first plates through the axle shafts. An installation includes a trolley and main line extending between two fixed anchorages. In use, the main line passes between the plates of the trolley, the main line contacts a sheave or pulley wheel of the trolley whereby the trolley can travel along the main line.